The president of the United States has, legally speaking, a ton of power. He can fire the head of the country’s federal investigative agency. He can decide, unilaterally, to give ultra-classified information to foreign leaders. He has essentially unconstrained authority to use nuclear weapons however he sees fit.

But what if the president’s closest advisers were to conclude he was unfit for office?

According to former Deputy FBI Director Andrew McCabe, Deputy Attorney General Rod Rosenstein briefly discussed just that possibility in 2017, in the days after President Donald Trump fired FBI director James Comey.

Specifically, that’s Section 4 of the 25th Amendment to the Constitution. The amendment states that if, for whatever reason, the vice president and a majority of sitting Cabinet secretaries decide that the president is “unable to discharge the powers and duties of his office,” they can simply put that down in writing and send it to two people — the speaker of the House and the Senate’s president pro tempore.

Then the vice president would immediately become “acting president,” and take over all the president’s powers.

Let that sink in — one vice president and any eight Cabinet officers can, theoretically, decide to knock the president out of power at any time.

If the president wants to dispute this move, he can, but then it would be up to Congress to settle the matter with a vote. A two-thirds majority in both houses would be necessary to keep the vice president in charge. If that threshold isn’t reached, the president would regain his powers.

Section 4 of the 25th Amendment has never been invoked in reality, though it’s a staple of thriller fiction. But there’s been a surge of interest in it throughout Trump’s presidency, as reports of the president’s bizarre behavior behind closed doors have piled up, and as his top officials have kept anonymously telling reporters that he’s unfit to govern.

Trump, for his part, responded to McCabe’s comments with fury, accusing him and Rosenstein of “planning a very illegal act.” And though it seems the discussions were brief and never went anywhere, from what we know, it does seem Rosenstein’s concerns were more about the president’s possible corruption and ties to Russia than his physical or mental health. (Rosenstein has since released a statement through the Justice Department saying that, “based on his personal dealings with the President, there is no basis to invoke the 25th Amendment.”)

Whatever the current circumstances, an enormous amount rests on any president of the United States’ fitness for office. The 25th Amendment does exist as a failsafe that can theoretically be used if any president truly does appear to be unfit — though one major challenge may be having the competence to carry it out without causing an even greater disaster.

1) Why was the 25th Amendment adopted?

The framers of the Constitution were farsighted about many things, but presidential succession was not among them. The text was vague on several matters, including on whether the vice president fully becomes president if the sitting president dies or resigns (in practice, the answer was interpreted as “yes”), and on how to fill a vice presidential vacancy in the middle of a term (in practice, the answer was interpreted as “you can’t”).

Most interestingly for our purposes, the Constitution’s original text states that a president could be removed from office for “inability” but gives zero specifics about how this would actually be determined or carried out. So when President James Garfield was bedridden after being shot and President Woodrow Wilson was debilitated by a stroke, they simply lingered on in the presidency without doing very much for months, because no one knew what else could be done while they were still drawing breath.

These scenarios may not have been so bad in the United States of the 1790s, but by the mid-20th century the country had become a global superpower, and modern communication tools created omnipresent demands for presidential decisions and actions.

The chaos and instability that followed John F. Kennedy’s assassination finally spurred Congress to move toward solving these problems. For once, it moved quickly, passing what became the 25th Amendment to the Constitution in 1965 and winning its ratification in the states by 1967.

The new amendment cleared up that yes, if a president died or resigned or was convicted of impeachment crimes, the vice president would fully become president. It provided, finally, for a simple way to fill a vacant vice presidency — the president nominates someone, and both Houses of Congress take a vote. It allowed for a president laid low by surgery or injury to voluntarily transfer their powers to the vice president and then easily get them back with a written declaration that he was healthy again.

And then there’s Section 4 — which is about how the vice president and a majority of the Cabinet can deprive the president of his or her powers without consent.

2) Wait, the VP and Cabinet can depose the president?

Sort of. There are three major parts to Section 4 of the 25th Amendment. The first part establishes how a president can be quickly stripped of his or her powers due to inability.

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.

A few notes here. First, the power to sideline the president for inability is given to the vice president and a “majority” of “the principal officers of the executive departments.” (President Reagan’s Justice Department interpreted this to mean the main Cabinet departments, which today number 15.) Theoretically, Congress can also create and empower some “other body” that could make this declaration, but so far it has not done so.

So all the vice president and eight Cabinet secretaries have to do is put in writing that the president is “unable” and send that message to the Speaker of the House (currently Nancy Pelosi) and the Senate’s president pro tem (currently Chuck Grassley (R-IA)). Then the vice president “immediately” takes on the president’s “powers and duties.”

Importantly, though, the veep only becomes “acting president.” So the elected president hasn’t lost their office yet, just their powers — and not necessarily permanently, as we’ll see in a moment.

Finally, there is zero elaboration on what it would mean for the president to be “unable to discharge the powers and duties of his office.” There is no specification even that it refers solely to health. In theory, it could entail not just physical inability but a judgment call on mental health or even, conceivably, poor character or simple disagreement. It’s really up to the VP and Cabinet to interpret it.

3) But what if the president wants to stay in charge?

Section 4 continues:

Thereafter, when the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and a majority of either the principal officers of the executive department or of such other body as Congress may by law provide, transmit within four days 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.

This is a mouthful, but the gist is that the president can tell the speaker of the House and Senate president pro tem that he or she are in fact not unable to perform their duties, and that he or she wants their powers back. You can imagine this happening if the president regains consciousness from some injury or ailment — or if he or she simply disagrees that they are unfit for office.

If the president does this, he or she would get their powers back in four days — unless the vice president and at least eight Cabinet officials say, in writing, that he is still unable. Then the vice president will remain in charge for the time being, and Congress will have to step in to settle this dispute. The rest of Section 4 is about this contingency:

Thereupon Congress shall decide the issue, assembling within forty-eight hours for that purpose if not in session. If the Congress, within twenty-one days after receipt of the latter written declaration, or, if Congress is not in session, within twenty-one days after Congress is required to assemble, determines by two-thirds vote of both Houses that the President is unable to discharge the powers and duties of his office, the Vice President shall continue to discharge the same as Acting President; otherwise, the President shall resume the powers and duties of his office.

So Congress would vote on whether the president is in fact “unable.” If two-thirds of both the House and Senate vote that he or she is, then the vice president would remain in charge as acting president.

If they fall short of that margin in either House, or simply fail to act within 21 days, the president would regain his or her powers.

4) In what situations might this actually be used?

Section 4’s text is broad and could apply to a spectrum of different circumstances.

The least controversial scenario would be if a president should become indisputably physically debilitated either from an injury or ailment, so much so that he couldn’t communicate but remained alive. Then it’s a no-brainer to use Section 4 to put the vice president in charge unless and until the president recovers.

But one can also imagine situations in which the president’s physical or mental health is the subject of some dispute — including from the president himself. As a 1988 Miller Center report put it:

In retrospect, [Section 4] probably could have applied to the final periods of Woodrow Wilson's or Franklin D. Roosevelt's presidencies. This provision involves a sick president who either refuses or is unable to confront his disability. Put another way, this section basically applies to a president who is disabled but unwilling to step aside. He or she may be stubborn, or be in the hands of a powerful staff or of a strong-willed spouse, the latter being Wilson's case.

Indeed, the topic came up among top administration officials during President Reagan’s second term. In early 1987, White House aide Jim Cannon became intensely disturbed by reports from staffers about how the president had been acting. As he later told Jane Mayer and Doyle McManus:

“They told stories about how inattentive and inept the President was. He was lazy; he wasn't interested in the job. They said he wouldn't read the papers they gave him, even short papers and documents. They said he wouldn't come over to work. All he wanted to do was to watch movies and television at the residence.”

So Cannon wrote a memo in which he urged White House Chief of Staff Howard Baker to “consider the possibility that section four of the 25th Amendment might be applied.” But it didn’t end up happening — Baker soon decided that Reagan was still in possession of his faculties, and the president remained in office for his full final two years. (Reagan suffered from Alzheimer’s in his later years, and some argue he demonstrated early symptoms while he was in office.)

Finally, the text of the amendment is so vaguely written that it could conceivably be invoked for any reason — even one unrelated to health — so long as enough Cabinet secretaries and the VP are in agreement and two-thirds of both the House and Senate later back them up. For this reason, Section 4 is a favorite of thriller writers concocting scenarios in which malefactors use some bogus pretext to depose the president.

Indeed, the senators who drafted the amendment openly acknowledged that if this power were to be utilized by “rogues,” it could result in “usurpation” of the presidency, as then-Sen. Birch Bayh wrote in a Judiciary Committee report on the proposal.

However, they hoped that since the Cabinet and vice president — “the persons closest to the president, both politically and physically” — are empowered to start this process, that would cut down on any incentives for coup-like mischief. Cabinet secretaries are appointed by the president, after all, so presumably they wouldn’t remove him from power without a really, really good reason. (The Gerald R. Ford Library has posted many fascinating primary source documents on the drafting and passage of the 25th Amendment online at this link.)

5) This sorta feels like a coup. Is it a coup?

“This was an illegal coup attempt on the President of the United States.” Dan Bongino on @foxandfriends True! — Donald J. Trump (@realDonaldTrump) February 18, 2019

Invoking the 25th Amendment would seem to not technically be a coup, because it’s part of the constitution.

Still, there’s zero precedent for this actually happening in US history, and the vast majority of Americans are likely unaware that it’s even possible. Even savvy political actors or entrenched institutional ones likely aren’t all that familiar with how the amendment is meant to work.

So if a sitting president were to be removed from power by a vice president and Cabinet despite the president’s objections, it would sure feel like a coup to a whole lot of people, regardless of the technical legality. And key actors close to the president could well respond like they’re facing a coup. For instance, what would the Secret Service do in this situation? The military?

This is particularly the case when the critique of the president isn’t primarily based on physical or mental health, but rather general “unfitness” — something that can be in the eye of the beholder.

If the vice president and Cabinet secretaries truly concluded that the president could not remain in office, they would need to document everything that led them to that conclusion and assemble an airtight public case. They would also need to be prepared for the sitting president to resist — either in the court of public opinion or otherwise.

Basically, things could get out of hand really fast. But if the vice president and Cabinet feel the situation is dire enough, it could be a risk worth taking.

6) What does all this mean for Trump?

From the beginning of his presidency, it was clear that Donald Trump was going to govern the same way he campaigned: with a tendency to pick fights and hold grudges, a lack of attention to detail (or, occasionally, fact), and a style that the New York Times has called “shoot-from-the-hip-into-his-own-foot.”

Perhaps the president is a basically rational person who just has a very strange and idiosyncratic personal style. Perhaps he’s just perfectly comfortable repeatedly lying about easily verifiable facts, or profoundly uninterested in examining evidence that conflicts with his assumptions.

But many of the critiques of Trump’s “unfitness” have subtext — and occasionally, outright text — alluding to his mental health.

“I think there is a subtext here that is unlike anything that I have seen in 50 years of being a reporter,” journalist Carl Bernstein said on CNN in 2017. “And that is that I am hearing from Republicans, and other reporters are as well, that there is open discussion by members of the president of the United States’ own party about his emotional maturity, stability.” He added: “We are in uncharted territory here.”

Conservative New York Times columnist Ross Douthat wrote a May 2017 column calling for the Cabinet to invoke the 25th Amendment, and put it more bluntly: “The presidency now has kinglike qualities, and we have a child upon the throne.”

Diagnosing the president’s mental health from afar is a bad idea, as political partisans can see what they want to see, and the American Psychiatric Association has long cautioned even professional psychiatrists against evaluating anyone they haven’t personally examined.

Furthermore, the actual reported discussion of the 25th Amendment by Rosenstein and others doesn’t seem to have been based on “mental health” specifically, but rather on fears of the president’s corruption or possible compromise by Russia.

Yet that’s precisely why the 25th Amendment gives the power to the vice president and the Cabinet secretaries here. Their judgments won’t be skewed by bias against the president’s party. They work with the president up close and see him in private. So if they see deeply troubling things, they are the ones who have the ability — and, arguably, the responsibility — to act.

This article was originally published in 2017. It has been updated to reflect recent news.