There are two ways to remove an American president from office. One is impeachment, which requires a trial conducted by Congress. The other involves enacting the 25th Amendment.

In 1965, Congress passed the 25th Amendment to the U.S. Constitution, which changed a portion of Article II, Section 1. The Amendment was understandable given what the country had just gone through. An assassin gunned down President John F. Kennedy and the nation needed to update century-old succession protocols.

The 25th Amendment includes four sections.

Section 1 is simple, direct and clear. It says, “In case of the removal of the President from office or of his death or resignation, the Vice President shall become President.” It formalized the historical process that had long been followed.

Section 2 says if the vice president becomes president, the new president names the No. 2 person and Congress affirms by a simple majority. “Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.” Note that this section gives Congress and the new president shared authority in naming a vice president since the public didn’t vote for this person.

Section 3 is for when presidents decide they cannot do the job. Maybe they are going to undergo surgery, for example. It sets up a notification system so Congress is kept in the loop: “Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President.”

Section 4 is the section that is in the headlines today. It is the part of the amendment that sets up a protocol for others to intervene to say the president is unable to fulfill the duties of the office. The section begins with who can intervene. The vice president has to be willing to go along and then get the majority of the cabinet to sign on to removing the president.

Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.

Section 4 provides a way for the president to try to resume power by sending a note to the leaders of the House of Representatives and the Senate that “no inability exists.” It would then be up to Congress to decide what to do next. Congress could take up to 21 days to render a decision and then both houses would have to vote by a two-thirds margin to remove the president.

While the decision is in play, the vice president would be the acting president, so there is that avenue to neuter Donald Trump’s power in the two weeks before Joe Biden takes office. But Vice President Mike Pence and the majority of the cabinet would have to bring the allegation against the president.

A two-thirds margin is a nearly unimaginable feat in a divided Congress. It is, of course, meant to be a high bar so Congress does not just try to unseat a president whenever Congress is unhappy.

Why did we need this amendment?

The Constitution set out the line of succession in the case of the death of a president, but it was less clear about how to go about removing a president and how we should go about replacing a vice president. It is not an academic exercise. Seven vice presidents have died in office and one vice president resigned.

What’s more, USA Today pointed out, is that when a vice president leaves or dies in office, the people in line to move up to the vice president’s job might not be the best choice, all things considered:

Lyndon B. Johnson’s ascension to the presidency meant that — for the 16th time — the country had no vice president. And there was no tested way of dealing with a severe presidential illness. Johnson previously had suffered a heart attack and the next two people in line to be president were the 71-year-old speaker of the House and the 86-year-old president pro tempore of the Senate.

The Cornell Law School explained:

But the seemingly most insoluble problem was that of presidential inability—Garfield’s lying in a coma for eighty days before succumbing to the effects of an assassin’s bullet, Wilson an invalid for the last eighteen months of his term, the result of a stroke—with its unanswered questions: who was to determine the existence of an inability, how was the matter to be handled if the President sought to continue, in what manner should the Vice President act, would he be acting President or President, what was to happen if the President recovered. Congress finally proposed this Amendment to the states in the aftermath of President Kennedy’s assassination, with the Vice Presidency vacant and a President who had previously had a heart attack.

How have we used the 25th Amendment?

It has come into play more than you might think.

In the 1970s, we saw two people come to the top two offices without ever being elected to the job.

Application 1: Vice President Spiro Agnew resigned (Oct. 10, 1973) so President Richard Nixon nominated Gerald Ford to become vice president.

Application 2: President Nixon resigned and new Vice President Gerald Ford became president.

Application 3: President Ford nominated, and Congress confirmed, Nelson A. Rockefeller to be vice president.

Application 4: Section 3 came into play when Ronald Reagan underwent surgery in 1985.

Application 5 and 6: George W. Bush handed over authority to Vice President Dick Cheney when President Bush went under anesthesia in 2002 and 2007.

How is the 25th Amendment different from impeachment?

The impeachment process is a tool Congress can use to remove or censure a president without the vice president’s support. It is more like a trial on charges of treason, bribery or “other high crimes and misdemeanors.” The House determines if there is cause for a trial and the Senate decides whether to hold a trial. A simple majority of the House has to vote for impeachment, but it takes a two-thirds majority of the Senate to convict and remove a president from office. That has never happened.