" Make America Great Again " ( MAGA ) is a campaign slogan used in American politics that was popularized by President Donald Trump in his 2016 presidential campaign. President Ronald Reagan used the similar slogan " Let's Make America Great Again " in his 1980 presidential campaign.
1980 Reagan presidential campaign
"Let's Make America Great Again" was first used in President Ronald Reagan's 1980 presidential campaign, when the United States was suffering from a worsening economy at home marked by stagflation.     Using the country’s economic distress as a springboard for his campaign, Reagan used the slogan to stir a sense of patriotism among the electorate.
Use by Bill Clinton
The phrase was also used in speeches  by Bill Clinton during his 1992 presidential campaign ; however, it was not a slogan of the campaign.  Clinton also used the phrase in a radio commercial aired for Hillary Clinton's 2008 presidential primary campaign. 
2016 Trump presidential campaign
In December 2011, Trump made a statement in which he said he was unwilling to rule out running as a presidential candidate in the future, explaining "I must leave all of my options open because, above all else, we must make America great again".  Two months earlier, Roger Stone, Trump's longtime political advisor and a veteran of Reagan's 1980 campaign, tweeted the slogan: "Make America Great Again --TRUMP HUCKABEE 2012 #nomormons". 
Trump himself began using the slogan formally on November 7, 2012, the day after Barack Obama won his reelection against Mitt Romney. He first considered "We Will Make America Great", but did not feel like it had the right "ring" to it.  "Make America Great" was his next name, but upon further reflection, he felt that it was a slight to America because it implied that America was never great. After selecting "Make America Great Again", Trump immediately had an attorney register it. (Trump later said that he was unaware of Reagan's use in 1980 until 2015, but noted that "he didn't trademark it".)  On November 12 he signed an application with the United States Patent and Trademark Office requesting exclusive rights to use the slogan for political purposes. It was registered as a service mark on July 14, 2015, after Trump formally began his 2016 presidential campaign and demonstrated that he was using the slogan for the purpose stated on the application.   
Some people think that the slogan is so well written that it helped him win the presidency (and similarly helped Reagan win in 1980).
During the campaign, Trump often used the slogan, especially by wearing hats emblazoned with the phrase in white letters, which soon became popular among his supporters.  The slogan was so important to the campaign that it spent more on making the hats – sold for $25 each on its website – than on polling, consultants, or television commercials; the candidate claimed that "millions" were sold.  Following Trump's election, the website of his presidential transition was established at greatagain.gov.  The president stated in January 2017 that the slogan of his 2020 reelection campaign would be "Keep America Great!", immediately ordering a lawyer to trademark it. 
Social media usage
Donald Trump took the campaign slogan to social media (primarily Twitter), using the hashtags #makeamericagreatagain and its abbreviation #maga. In response to criticism regarding his frequent and untraditional usage of social media, Trump defended himself by tweeting "My use of social media is not Presidential - it’s MODERN DAY PRESIDENTIAL. Make America Great Again!" on July 1, 2017.  . This comment justified his usage of social media as main method of communicating to his base.
In the first half of 2017 alone, Trump has repeated his slogan on Twitter 33 times.  In an article for Bloomberg, Whitehouse noted "A regression analysis suggests the phrase adds (very roughly) 51,000 to a post's retweet-and-favorite count, which is a big deal given that the average Trump tweet attracts a total of 107,000." 
Trump attributed social media to his victory when he said "I won the 2016 election with interviews, speeches, and social media."  According to RiteTag, the estimated hourly statistics for #maga on Twitter alone include: 1304 unique tweets, 5,820,000 hashtag exposure, and 3424 retweets with 14% of #maga tweets including images, 55% including links, and 51% including mentions.  Note: these figures would be even greater if all derivatives of the slogan across all social media platforms were taken into account.
Donald Trump created his Twitter account in March, 2009. His follower count increased significantly following his announcement to run for president in the 2016 presidential election, with particularly notable spikes occurring after both securing the Republican party nomination and winning the presidency. 
Trump's Twitter handle is @realDonaldTrump, and his account had 42.2M followers as of November 8, 2017. 
Use by others
After Donald Trump popularized the use of the phrase, the phrase and modifications of it became widely used to refer to his election campaign and his politics. Trump's primary opponents, Ted Cruz and Scott Walker, began using "Make America Great Again" in speeches, inciting Trump to send cease-and-desist letters to them. Trump claimed after the election that the hats "were copied, unfortunately. It was knocked off by 10 to one ... but it was a slogan, and every time somebody buys one, that's an advertisement".  Cruz later sold hats featuring, "Make Trump Debate Again", in response to Trump's boycotting the Iowa January 28, 2016 debate. 
In June 2017, Emmanuel Macron, President of France, rebuked Trump over withdrawing from the Paris Climate Agreement. The last sentence of the speech delivered by him was "make our planet great again". 
In art, entertainment, and media
The most widespread use of the phrase and its variants were in media, especially television comedies. For example:
- In the South Park episode " Where My Country Gone? " (2015), supporters of Mr. Garrison, who runs a campaign that is a parody of Trump's, are seen holding signs bearing the slogan. 
- John Oliver spoofed the slogan in a segment of his show, urging viewers to "Make Donald Drumpf Again" in reference to the original name of Trump's ancestors.   The segment broke HBO viewership records, garnering 85 million views. 
- Make Everything Great Again is a street art mural by artist Mindaugas Bonanu in Vilnius, Lithuania. 
- Comedian David Cross' 2016 stand-up tour was titled "Making America Great Again" 
- Fall Out Boy's remix album was named Make America Psycho Again 
- Snoop Dogg released a song titled Make America Crip Again 
- Make America Rock Again was a rock concert tour 
- WWE star Darren Young and former star Bob Backlund began appearing on WWE TV in May 2016 with Backlund acting as Young's life coach, promising to "Make Darren Young Great Again".  
- The slogan was also modified for use in commercial contexts such as film posters and advertisements. The tagline for the film, The Purge: Election Year , was "Keep America Great" (also the slogan for Trump's aforementioned reelection campaign).  2017 Syfy film Sharknado 5: Global Swarming was released with the tagline "Make America Bait Again".  A Dunk-a-roos marketing campaign used the slogan "Make America Dunk Again". 
- Singer Joy Villa produces single 'Make America Great Again' a few months after she appears at the 2017 Grammy Awards in a 'MAGA' Dress. 
- In 2016, two Dragon Con cosplayers, claiming an association with Adult Swim and Cartoon Network dressed as the World Trade Center during the September 11 attacks, wore "Make FishCenter Great Again" hats.   
- The 2017 video game Wolfenstein: The New Colossus used "Make America Nazi-Free Again" in it"s marketing campaign.