Since the 2000 United States presidential election, red states and blue states have referred to states of the United States whose voters predominantly choose either the Republican Party (red) or Democratic Party (blue) presidential candidates. Since then, the use of the term has been expanded to differentiate between states being perceived as liberal and those perceived as conservative.
All states contain both liberal and conservative voters (i.e., are "purple") and only appear red/blue on the electoral map because of the winner-take-all system used by most states in the Electoral College.   However, the perception of some states as "red" and some as "blue" was reinforced by a degree of partisan stability from election to election—from the 2000 election to the 2004 election, only three states changed "color", and as of 2016 fully 38 out of 50 states have voted for the same party in every presidential election since the red/blue terminology was popularized in 2000.
The choice of colors reverses a long-standing convention of political colors whereby red symbols (such as the Red Flag or Red Star) are associated with left-wing politics, and right-wing movements often choose blue as a contrasting color.  Indeed, until the 1980s, Republicans were often represented by blue and Democrats by red. The current terminology of "red states" and "blue states" came into use in the United States presidential election of 2000 on an episode of the Today show on October 30, 2000. According to The Washington Post, the terms were coined by journalist Tim Russert, during his televised coverage of the 2000 presidential election.  That was not the first election during which the news media used colored maps to depict voter preferences in the various states, but it was the first time a standard color scheme took hold; the colors were often reversed or different colors used before the 2000 election.
Origins of the color scheme
Before the 2000 presidential election, the traditional color-coding scheme was often "Blue for Republican, Red for Democrat,"  in line with European associations, where red is used for left-leaning parties, and blue for the right.  The colors red and blue also are featured on the U.S. flag. Traditional political mapmakers, at least throughout the 20th century, have used blue to represent the modern-day Republicans, as well as the earlier Federalist Party. This may have been a holdover from the American Civil War, during which the predominantly Republican north was considered "blue".  However, at that time, a maker of widely-sold maps accompanied them with blue pencils in order to mark Confederate force movements, while red was for the union. 
Even earlier, in the 1888 presidential election, Grover Cleveland and Benjamin Harrison used maps that coded blue for the Republicans, the color perceived to represent the Union and " Lincoln's Party", and red for the Democrats.  The parties themselves had no official colors, with candidates variously using either or both of the national color palette of red and blue (white being unsuitable for printed materials).
There was one historical use, associated with boss rule, of blue for Democrats and red for Republicans: in the late 19th century and early 20th century, Texas county election boards used color-coding to help Spanish speakers and illiterates identify the parties;  however, this system was not applied consistently in Texas and was not replicated in any other state. In 1908, The New York Times printed a special color map, using blue for Democrats and yellow for Republicans, to detail Theodore Roosevelt's 1904 electoral victory.  That same year, a color supplement included with a July issue of the Washington Post used red for Republican-leaning states, blue for Democratic-leaning states, yellow for "doubtful" states, and green for territories, which had no presidential vote. 
The advent of color television prompted television news reporters to rely on color-coded electoral maps, though sources conflict as to the conventions they followed. One source claims that in the six elections prior to 2000 every Democrat but one had been coded red. It further claims that from 1976 to 2004, the broadcast networks, in an attempt to avoid favoritism in color-coding, standardized on the convention of alternating every four years between blue and red the color used for the incumbent party.  
According to another source, in 1976, John Chancellor, the anchorman for NBC Nightly News, asked his network's engineers to construct a large illuminated map of the United States. The map was placed in the network's election-night news studio. If Jimmy Carter, the Democratic candidate that year, won a state, it would light up in red; if Gerald Ford, the incumbent Republican president, carried a state, it would light up in blue. The feature proved to be so popular that, four years later, all three major television networks would use colors to designate the states won by the presidential candidates on Election Night, though not all using the same color scheme. NBC continued to use the color scheme employed in 1976 for several years. NBC newsman David Brinkley famously referred to the 1980 election map outcome showing Republican Ronald Reagan's 44-state landslide as resembling a "suburban swimming pool". 
CBS, from the 1984 election on, used the opposite scheme: blue for Democrats, red for Republicans. ABC used yellow for Republicans and blue for Democrats in 1976. However, in 1980 and 1984, ABC used red for Republicans and blue for Democrats. In 1980, when independent John B. Anderson ran a relatively high-profile campaign as an independent candidate, at least one network provisionally indicated that they would use yellow if he were to win a state. Similarly, in 1992 and 1996, at least one network would have used yellow to indicate a state won by Ross Perot; neither of them did claim any states in any of these years.
By 1996, color schemes were relatively mixed, as CNN, CBS, ABC, and The New York Times referred to Democratic states with the color blue and Republican ones as red, while Time and The Washington Post used an opposite scheme.    NBC used the colour blue for the incumbent party, which is why the Democrats were represented by Blue in 2000.
In the days following the 2000 election, whose outcome was unclear for some time after election day, major media outlets began conforming to the same color scheme because the electoral map was continually in view, and conformity made for easy and instant viewer comprehension. On Election Night that year, there was no coordinated effort to code Democratic states blue and Republican states red; the association gradually emerged. Partly as a result of this eventual and near-universal color-coding, the terms "red states" and "blue states" entered popular use in the weeks following the 2000 presidential election. After the results were final, journalists stuck with the color scheme, as The Atlantic' s December 2001 cover story by David Brooks entitled, "One Nation, Slightly Divisible", illustrated. 
Thus, red and blue became fixed in the media and in many people's minds, despite the fact that no official color choices had been made by the parties.  Some Republicans argue the GOP should retain its historic link with blue, since most center-right parties worldwide are associated with blue. On March 14, 2014, the California Republican Party officially rejected Red and adopted Blue as its color. Archie Tse, The New York Times graphics editor who made the choice when the Times published its first color presidential election map in 2000, provided a nonpolitical rationale, explaining that "Both 'Republican' and 'red' start with the letter 'R.'" 
There are several problems in creating and interpreting election maps that should be taken into account. Popular vote data is necessarily aggregated at several levels, such as counties and states, which are then colored to show election results. Maps of this type are called choropleth maps, which have several well-known problems that can result in interpretation bias. One problem arises when areal units differ in size and significance, as is the case with election maps. These maps give extra visual weight to larger areal units, whether by county or state. This problem is compounded in that the units are not equally significant. A large county or state may have fewer voters than a small one, for example. Some maps attempt to account for this by using cartogram methods, but the resulting distortion can make such maps difficult to read.   Another problem relates to data classification. Election maps often use a two-class color scheme (red and blue), which results in a map that is easy to read but is highly generalized. Some maps use more classes, such as shades of red and blue to indicate the degree of election victory. These maps provide a more detailed picture, but have various problems associated with classification of data. The cartographer must choose how many classes to use and how to break the data into those classes. While there are various techniques available, the choice is essentially arbitrary. The look of a map can vary significantly depending on the classification choices. The choices of color and shading likewise affect the map's appearance. Further, all election maps are subject to the interpretation error known as the ecological fallacy. 
Finally, there are problems associated with human perception.  Large areas of color appear more saturated than small areas of the same color.  A juxtaposition of differing colors and shades can result in contrast misperceptions. For example, due to the simultaneous contrast effect, the Bezold effect, and other factors, an area shaded light red surrounded by areas shaded dark red will appear even lighter. Differing shades of red and blue compound this effect. 
Cartographers have traditionally limited the number of classes so that it is always clear which class a color shade represents. Some election maps, however, have broken this tradition by simply coloring each areal unit with a red-blue mixture linked to voting ratio data—resulting in an "unclassified choropleth map". These "purple maps" are useful for showing the highly mixed nature of voting, but are extremely difficult to interpret in detail. The lack of clear classes make these purple maps highly prone to the problems of color perception described above. However, there are pros and cons to both classified and unclassified choropleth maps. Each tend to bring out some patterns while obscuring others.  All these points should be taken into account when looking at election maps.
The paradigm has come under criticism on a number of fronts. Many argue that assigning partisanship to states is only really useful as it pertains to the Electoral College, primarily a winner-take-all system of elections (with the exceptions of Nebraska and Maine).
The Republican and Democratic parties within a particular state may have a platform that departs from that of the national party, sometimes leading that state to favor one party in state and local elections and the other in Presidential elections. This is most evident in the Southern United States, where the state Democratic Party organizations tend to be more conservative than the national party, especially on social issues. Likewise, Republicans have elected a number of statewide officeholders in states that are solidly blue at the presidential level, such as New York, Vermont, Illinois, and Hawaii.
Arkansas and West Virginia were won by George W. Bush in 2004, but the Democrats at the time held all four U.S. Senate seats and the majority of elected executive officeholders in those states; similarly, Tennessee went solidly for Bush in both 2000 and 2004, but going into 2004, its Governor was a Democrat and both chambers of the state legislature were controlled by Democrats. The converse can also be true, as in the case of Maine, which had two Republican U.S. Senators but voted for John Kerry in 2004. Likewise, Vermont, New York, Massachusetts, Maryland, and Hawaii voted for Kerry by wide margins, but all had Republican governors at the time of the election.
In his address before the 2004 Democratic National Convention, Barack Obama rejected the division of the United States into red states and blue states, saying: "The pundits like to slice-and-dice our country into red states and blue states—red states for Republicans, and blue states for Democrats. But I've got news for them, too. We worship an awesome God in the blue states, and we don't like federal agents poking around our libraries in the red states. We coach Little League in the blue states and have gay friends in the red states. … We are one people, all of us pledging allegiance to the stars and stripes, all of us defending the United States of America." 
In April 2008, Republican presidential nominee John McCain predicted that the 2008 presidential election would not follow the red state/blue state pattern, saying, "I'm not sure that the old red state, blue state scenario that prevailed for the last several elections works. I think most of these states that we have either red or blue are going to be up for grabs."  Arguably, this eventually proved to be somewhat true, although not in McCain's favor, as Barack Obama won three "red" states that had not voted Democratic in many years, namely Virginia, North Carolina, and Indiana. Obama also came close to winning Missouri, losing it by a 0.2% margin. Notably, however, the only deviations from the preexisting red-blue paradigm were all in Obama's favor.
A purple state refers to a swing state where both Democratic and Republican candidates receive strong support without an overwhelming majority of support for either party. Purple states are also often referred to as battleground states.
The demographic and political applications of the terms have led to a temptation to presume this arbitrary classification is a clear-cut and fundamental cultural division. Given the general nature and common perception of the two parties, "red state" implies a conservative region or a more conservative American, and "blue state" implies a more liberal region or a more liberal American. But the distinction between the two groups of states is less simplistic. The analysis that suggests political, cultural, and demographic differences between the states is more accurate when applied to smaller geographical areas.
Traditionally, the practice of designating a U.S. state as "red" or "blue" is based on the "winner-take-all" system employed for presidential elections by 48 of the 50 U.S. states and the District of Columbia. (Electoral law in Maine and Nebraska makes it possible for those states to split their electoral votes.)
Despite the prevalent "winner-take-all" practice, the minority always gets a sizable vote. While the red/blue paradigm encourages hardening into ideological camps, political parties, candidates in those parties and individuals members of those parties have a variety of positions and outlooks—nearly every town, city and patch of farmland in the country is "purple", a mix of neighbors, friends and family, each of whose own mixed political preferences tip the scale to vote for one side or the other in a contest. Individually and collectively, they are not reducible to red or blue. 
An emerging area of science that includes network theory, complexity science and big data is changing the way we see and understand complex systems and massive amounts of information by allowing us to see and analyze massive detail. One example is Mark Newman's election results maps,  which change from a red/blue paradigm to one of shades of purple. 
All states were consistent in voting for George W. Bush or his Democratic Party opponent in the 2000 and 2004 presidential elections, except for three: New Mexico (Al Gore in '00 and Bush in '04); Iowa (Gore in '00 and Bush in '04); and New Hampshire (Bush in '00 and Kerry in '04). The 2004 election showed two of these three states to be true to the presidential preferences of their respective regions, creating a greater regional separation; thus, an argument that the country was more divided from the 2000 election. All three of those states were very close in both elections. In 2008, Obama carried Iowa and New Hampshire by more than nine percentage points, and New Mexico by double digits.
During the Bush administration, the red-blue map was criticized by some for exaggerating the perceived support for President Bush. In the 2000 election, Bush received a smaller share of the popular vote than Al Gore, and four years later defeated John Kerry in this count by less than two and a half percentage points. However, because of the large geographical size of many states in the Central and Southern United States, the color-coded map appeared to show a huge tide of support for Bush and the Republicans with thin outliers of Democratic support on the coasts and near the Great Lakes. 
In reality, many of the Great Plains and Rocky Mountain states which voted for Bush are relatively sparsely populated (Nebraska, for instance, has a population similar to the island of Manhattan). While the "blue states" represented a comparatively small geographic area, they contained large populations, which ended up making President Bush's national level of support slimmer than the red–blue map would seem to indicate. Various different maps, such as ones which coded states based on the strength of their support for one candidate or another, ones which gave results based on county, or ones which displayed states according to the size of their population, were proposed as correctives to this perceived flaw.
Feelings of cultural and political polarization between red and blue states, which have gained increased media attention since the 2004 election, have led to increased mutual feelings of alienation and enmity.  Polarization is more evident on a county scale. Nearly half of U.S. voters resided in counties that voted for Bush or Kerry by 20 percentage points or more in 2004. By comparison, only a quarter of voters lived in such counties in 1976. 
The polarization has been present for only three close elections (2000, 2004, and 2016). In the 1996 election, 31 U.S. states were "blue" (i.e., they voted for Democrat Bill Clinton) and 19 "red" (i.e., they voted for Republican Bob Dole) (though at the time the current color scheme was not as universal as today). One trend that has been true for several election cycles is that states that vote Republican tend to be more rural and more sparsely populated (thus having fewer electoral votes) than states that vote Democratic.
Although the Electoral College determines the Presidential election, a more precise measure of how the country actually voted may be better represented by either a county-by-county or a district-by-district map. By breaking the map down into smaller units (including many " blue counties " lying next to " red counties "), these maps tend to display many states with a purplish hue, thus demonstrating that an ostensibly "blue" or "red" state may, in fact, be closely divided. Note that election maps of all kinds are subject to.
These county-by-county and district-by-district maps reveal that the true nature of the divide is between urban areas / inner suburbs and suburbs / rural areas. For example, in the 2008 elections, even in "solidly blue" states, the majority of voters in most rural counties voted for Republican John McCain (good examples would be Minnesota, New York, and Maryland), with some exceptions.
In "solidly red" states, a majority of voters in most urban counties voted for Democrat Barack Obama; good examples for this would be Dallas County, Texas and Fulton County, Georgia (the homes of major U.S. cities Dallas and Atlanta, respectively). Both provided Obama with double-digit margins of victory over McCain. An even more detailed precinct-by-precinct breakdown demonstrates that in many cases, large cities voted for Obama, but their suburbs were divided.
Red states and blue states have several demographic differences from each other. The association between colors and demographics was notably made in a column by Mike Barnicle, and reinforced in a controversial response from Paul Begala, though the association between demographics and voting patterns was well known before that.
In the 2008 elections, both parties received at least 40% from all sizable socioeconomic demographics, except that McCain (Republican) received 37% from voters earning $15,000–$30,000, and 25% from voters earning under $15,000, according to exit polling. In 2008, college graduates were split equally; those with postgraduate degrees voted for Obama by an 18% margin. By household income, Obama got a majority of households with less than $50,000 in annual income.
McCain got a slight majority (52% to 47%) of households consisting of married couples; Obama led almost 2–1 (65% to 33%) among unmarried voters. McCain held the more suburban and rural areas of both the red and blue states, while Obama received the large majority of the urban city areas in all the states. Independent candidate Ralph Nader did not win any electoral college votes, yet he received 2% of the vote of voters from high-income households and voters with graduate degrees.
Rate of union membership
Age, sex, and marital status
In terms of age, sex, and marital status, it is thought young adults under age 40 went for Obama. More married men voted for McCain, but more single men voted for Obama. The same went for women, but a higher percentage of women voted for Obama than McCain. The main constituency for McCain was white middle-aged married males. In terms of religion, Catholics and Protestant Christians were more likely to vote for McCain than Obama, whereas a higher rate of secular atheists, agnostics and other religious votes went for Obama.
2016 Exit polls
|Under $30k||$30k–$50k||$50k–$100k||$100k–$200k||$200k–$250k||$250k or more|
|Demographic||Age||Marital status||Sexual orientation|
|18-29||30-44||45-64||65 and over||Married||Unmarried||LGBT||Non-LGBT|
|Male||Female||High school or less||Some College||College graduate||Postgraduate|
|Demographic||Vote by race||Religion|
Table of presidential elections by states since 1972
Republican win over 5% Republican win under 5% Democratic win over 5% Democratic win under 5% Electoral college winner
|Democratic candidate||George McGovern||Jimmy Carter||Jimmy Carter||Walter Mondale||Michael Dukakis||Bill Clinton||Bill Clinton||Al Gore||John Kerry||Barack Obama||Barack Obama||Hillary Clinton|
|Republican candidate||Richard Nixon||Gerald Ford||Ronald Reagan||Ronald Reagan||George H. W. Bush||George H. W. Bush||Bob Dole||George W. Bush||George W. Bush||John McCain||Mitt Romney||Donald Trump|
|National popular vote||Nixon||Carter||Reagan||Reagan||Bush||Clinton||Clinton||Gore||Bush||Obama||Obama||Clinton|
|District of Columbia||McGovern||Carter||Carter||Mondale||Dukakis||Clinton||Clinton||Gore||Kerry||Obama||Obama||Clinton|
|Maine||Nixon||Ford||Reagan||Reagan||Bush||Clinton||Clinton||Gore (at-large and ME-01)||Kerry||Obama||Obama||Clinton (at-large)|
|Gore (ME-02)||Trump (ME-02)|
|Nebraska||Nixon||Ford||Reagan||Reagan||Bush||Bush||Dole||Bush||Bush||McCain (at-large, NE-01, NE-03)||Romney||Trump (at-large, NE-01, NE-03)|
|Obama (NE-02)||Trump (NE-02)|
: Split their votes.
The "Democratic blue" and "Republican red" color scheme is now part of the lexicon of American journalism.
Neither party national committee has officially accepted these color designations, though informal use by each party is becoming common. Both parties have since adopted logos that use their respective colors (a blue "D" for Democrats,  and a white "GOP" with a red elephant for Republicans). National conventions for both major parties increasingly feature the parties' respective colors, from the colors emphasized on convention podiums to the color conventioneers can be seen wearing on the delegate floor. The Democratic Congressional Campaign Committee also alluded the color scheme when it launched a national "Red to Blue Program" in 2006. 
The scheme has found acceptance and implementation from the U.S. Federal Government, as the Federal Election Commission report for the 2004 presidential election uses the red-Republican, blue-Democratic scheme for its electoral map. 
The choice of colors in this divide may appear counter-intuitive to foreign observers, as in most countries, red is associated with left-of-center parties, while blue is associated with conservative parties. For example, the major center-right parties in the United Kingdom, Canada, Australia, New Zealand, Italy, Spain and France all use blue or its shades (whether officially or unofficially); whereas the major center-left parties in each country are associated with red. If the U.S. followed such a pattern, blue would be used for the Republicans and red for the Democrats. However, the current U.S. scheme has become so ingrained in the American election system that foreign sources who cover U.S. elections, such as the BBC, Der Spiegel and El Mundo follow with the red-Republican, blue-Democratic scheme for U.S. elections.