Prior to the 25th Amendment, presidential succession procedures existed, but they were vague and didn’t cover every contingency. Assumedly, the vice president would become president if the president died or resigned.

However, it wasn’t clear what should happen if the president was temporarily incapacitated or if the vice president was incapacitated. The 25th Amendment sought to address these concerns.

The original Constitution allowed for the vice president to become acting president if the president died, resigned or became debilitated, but it didn’t state who had the power to declare the president unfit to serve or prevent the president from returning to office.

In addition, it didn’t specify if an acting president should take over the “Office of the President” or only perform presidential duties until the president returned or a qualified replacement was found.

READ MORE: US Presidents Who Became Ill or Incapacitated While in Office

The Constitution also didn’t indicate who would assume the vice-presidency if the vice president became president, died or was debilitated. It only said that Congress could declare, “what Officer shall then act as President.”

In February 1792, Congress passed the Presidential Succession Act, placing the Majority Leader of the House of Representatives and the President Pro Tempore of the Senate in the line of succession.

In 1886, Congress removed the President Pro Tempore and the House Majority Leader from the line of succession and replaced them with members of the presidential cabinet in order of rank, beginning with the Secretary of State.

In 1943, the 20th Amendment cleared the way for the vice-president elect to become president if the president-elect died or was debilitated. In 1947, Congress reinstated the Speaker of the House and the President Pro Tempore to the line of succession ahead of the president’s cabinet members.

Whether all these changes were done in the best interest of American citizens, or to take advantage of a crisis and control who ruled the White House, is still a matter of debate.

Until the 25th Amendment, each administration came up with its own plan to handle presidential and vice-presidential vacancies and reinstatement. This ambiguity led to confusion, ambiguity and in some cases, deceit.

For instance, in 1841, President William Harrison became the first president to die in office; vice president John Tyler succeeded him. Harrison’s cabinet gave Tyler the title, “Vice President Acting President,” but Tyler wanted more.

He moved into the White House, had himself sworn in as president and assumed full presidential powers, including giving an Inaugural Address. Despite some controversy, Congress eventually confirmed Tyler’s presidency.

In 1919, after having a series of strokes and ignoring warning signs of ill-health and neurological problems, President Woodrow Wilson had a massive stroke from which he never recovered during his presidency.

When his Cabinet suggested the vice president take over, Wilson’s wife Edith and his doctor, Cary Grayson, conspired to keep his condition a secret from both Congress and the public, leaving the United States without a competent leader.

After suffering heart problems and a mild stroke, President Dwight D. Eisenhower wrote a confidential letter to Vice President Richard M. Nixon instructing him on what to do if he was incapacitated. Eisenhower identified Nixon as the person who should determine his inability to perform his duties.

The letter wasn’t legal, however, and although Nixon became acting president when Eisenhower had a heart attack in 1955 and again when he had surgery in 1956, Nixon was never sworn in as president during Eisenhower’s terms.

The need for a succession amendment came to light when President John F. Kennedy was assassinated in Dallas, Texas, and there was confusion about whether Vice President Lyndon B. Johnson had also been injured and, if so, who would take their places in the line of succession.

On January 1, 1965, less than two years after the assassination of Kennedy, joint resolutions were introduced in the House and Senate recommending a succession amendment. By April, the House and Senate had approved their own versions and a committee created to resolve their differences.

On July 6, Congress passed a joint resolution and forwarded it to the states for ratification. The 25th amendment was ratified on February 10, 1967. President Johnson signed the 25th Amendment into law on February 23, 1967.

The amendment has the following four sections:

Section 1 states that if the president dies or resigns, the vice president shall become president.

Section 2 states that in the event of a vice-presidential vacancy, the president will nominate a vice president who will be confirmed by a majority Congressional vote.

Section 3 states that if the president tells the president pro tempore of the Senate and the speaker of the House in writing that he is unable to perform his presidential powers and duties, the duties shall fall to the vice president as acting president until the president notifies them in writing otherwise.

As acting president, the vice president is not sworn in as president; the president keeps his designation and the right to return.

Section 4 stipulates that when the vice president and a majority of a body of Congress declare in writing to the president pro tempore of the Senate and the Speaker of the House that the president is unable to perform the duties of the office, the vice president immediately becomes acting president.

The president can then submit a written declaration to the contrary and resume presidential powers and duties—unless the vice president and a majority body of Congress declare in writing within four days that the president cannot perform his duties, in which case Congress will vote on the issue.

Section 4 of the 25th Amendment has never been used, although the Reagan administration came close. On March 30, 1981, after President Reagan was shot and undergoing surgery, his administration prepared the necessary papers to invoke the 25th Amendment and make Vice President George H.W. Bush acting president.

The papers were never signed, despite some members of Reagan’s administration, Congress and even his doctor advising otherwise.

In 1987, Ronald Reagan was described as inattentive, distracted, lazy and inept by several concerned members of his staff, who suggested invoking Section 4 to remove him from office.

His new chief of staff, Howard Baker, soon determined he was anything but incapacitated and took no action against Reagan. (Reagan was later diagnosed with Alzheimer’s disease.)

Portions of the 25th Amendment have been invoked several times.

In 1973, Spiro Agnew became the first vice president to resign due to scandal after being charged with political corruption. The 25th Amendment required then-President Richard Nixon to nominate a new vice president for Congressional approval. Nixon appointed Gerald Ford and Congress approved the nomination.

In August 1974, the 25th Amendment compelled Vice President Gerald Ford to become president after Nixon resigned. This left the vice presidency unoccupied, so Ford invoked the 25th amendment again and nominated Nelson Rockefeller to fill the vacancy.

On July 13, 1985, President Ronald Reagan used the 25th Amendment to transfer power to Vice President George H.W. Bush while he underwent surgery for colon cancer.

On June 29, 2002, President George W. Bush invoked Section 3 of the 25th Amendment prior to going under anesthesia for a colonoscopy and briefly made Vice President Dick Cheney the acting president. He did the same again when he had another colonoscopy in 2007.

During Donald Trump's term, some initiated dialog about invoking Section 4 of the 25th Amendment against him. Still, the 25th Amendment exists to protect the democratically-elected president and the line of succession. It makes it difficult to unseat a president without proven just cause and majority consensus.

An Ailing Ike: How Eisenhower’s Health Affected His Role in the 1960 Election. Archives.gov.
Is it Time to Talk About the 25th Amendment? CNN.
John Tyler. The White House.
List of Vice Presidents Who Served as “Acting President” Under the 25th Amendment. The American Presidency Project.
Presidential Succession. United States Senate.
The 25th Amendment: Section 4 and March 30, 1981. The Reagan Library Education Blog.
The Establishment and First Uses of the 25th Amendment. Ford Library Museum.
The Twenty-Fifth Amendment. National Constitution Center.
Twenty-Fifth Amendment, Presidential Vacancy, Disability, and Inability. Cornell University Law School Legal Information Institute.
Woodrow Wilson: Strokes and Denial. The University of Arizona Health Sciences Library.
Worrying About Reagan. The New Yorker.