The Assistant to the President for National Security Affairs (APNSA), commonly referred to as the National Security Advisor (NSA) or at times informally termed the NSC Advisor,^[2][3] is a senior aide in the Executive Office of the President, based at the West Wing of the White House, who serves as the chief in-house advisor to the President of the United States on national security issues. The National Security Advisor is appointed by the President and does not require confirmation by the Senate,^[4] but an appointment of a three or four-star general to the role requires Senate reconfirmation of military rank.^[5]

The National Security Advisor participates in meetings of the National Security Council (NSC) and usually chairs meetings of the Principals Committee of the NSC with the Secretary of State and Secretary of Defense (the meetings not attended by the President). The National Security Advisor is supported by NSC staff who produce research and briefings for the National Security Advisor to review and present, either to the National Security Council or directly to the President.

The influence and role of the National Security Advisor varies from administration to administration and depends not only on the qualities of the person appointed to the position, but also on the style and management philosophy of the incumbent President.^[6] Ideally, the National Security Advisor serves as an honest broker of policy options for the President in the field of national security, rather than as an advocate for his or her own policy agenda.^[7]

However, the National Security Advisor is a staff position in the Executive Office of the President and does not have line or budget authority over either the Department of State or the Department of Defense, unlike the Secretary of State and the Secretary of Defense, who are Senate-confirmed officials with statutory authority over their departments;^[8] but the National Security Advisor is able to offer daily advice (due to the proximity) to the President independently of the vested interests of the large bureaucracies and clientele of those departments.^[6]

In times of crisis, the National Security Advisor is likely to operate from the White House Situation Room or the Presidential Emergency Operations Center (as on September 11, 2001),^[9] updating the President on the latest events in a crisis situation.

The National Security Council was created at the start of the Cold War under the National Security Act of 1947 to coordinate defense, foreign affairs, international economic policy, and intelligence; this was part of a large reorganization that saw the creation of the Department of Defense and the Central Intelligence Agency.^[10][11] The Act did not create the position of the National Security Advisor per se, but it did create an executive secretary in charge of the staff. In 1949, the NSC became part of the Executive Office of the President.^[10]

Robert Cutler was the first National Security Advisor in 1953. The system has remained largely unchanged since then, particularly since President John Kennedy, with powerful National Security Advisors and strong staff but a lower importance given to formal NSC meetings. This continuity persists despite the tendency of each new president to replace the advisor and senior NSC staff.^[10]

President Richard Nixon's National Security Advisor, Henry Kissinger, enhanced the importance of the role, controlling the flow of information to the President and meeting him multiple times per day. Kissinger also holds the distinction of serving as National Security Advisor and Secretary of State at the same time from September 22, 1973, until November 3, 1975.^[10][11]

Brent Scowcroft is the only person to have held the job in two non-consecutive administrations: in the Ford administration and in the G.H.W. Bush administration. Robert Cutler also held the job twice, both times during the Eisenhower administration. Henry Kissinger holds the record for longest term of service (2,478 days). Michael Flynn holds the record for shortest term of service (24 days).

Three and four-star generals require Senate confirmation due to the statutory nature requiring Congress to appoint their military rank.^[5] The prior National Security Adviser, H. R. McMaster, is a three-star lieutenant general and his military rank was reconfirmed by the Senate on March 15, 2017.^[18][19] On Thursday, March 22, 2018, President Donald Trump announced, via Twitter, that McMaster would be replaced as the National Security Advisor by former U.S. Ambassador to the United Nations John R. Bolton, effective April 9, 2018.^[20] On September 10, 2019, President Trump announced on Twitter that he "informed John Bolton last night that his services are no longer needed at the White House", and that Bolton had resigned.^[21] On September 18, 2019, President Trump announced on Twitter that Robert C. O'Brien will become the next National Security Advisor.^[22]