fun fact: the 25th amendment has two sections which allow the vice president to take over from the current president: section 3 and section 4.

They've only been invoked three times, though one is debatable. In all three cases, it involved the president's butt.

Section 4 is the one everyone is talking about recently.
It's the one that lets the vice president take over because they've judged the president to be "unable to discharge the powers and duties of [their] office"

It has never been used, though there have been a couple cases where it was considered. Two with Reagan and two with Trump.

The first Reagan one was when he was shot, and rushed into surgery. It's been argued that it should have been invoked, but it mainly didn't happen because of timing (Bush was on a plane and by the time he landed, Reagan was out of surgery)

and later in Reagan's presidency it was considered because of his possible dementia. It never was, though, and he wasn't diagnosed with Alzheimer's disease until years after leaving office.

It's twice been suggested for use on Trump:
In 2017 after the firing of FBI Director James Comey, and recently after the events of January 6th.

But section 3 is different. It's basically a president triggering the power-transfer on themselves. The idea is that a president who is temporarily unable to do the job can transfer it to their vice president, and take it back when they're well again.

And the first time it was seriously considered was in 1978, when Jimmy Carter was planning to have hemorrhoid surgery.
In the end, he didn't invoke it.

So the first time it was actually used was in 1985, when Ronald Reagan was diagnosed with bowel cancer.
There was some weirdness about how the official declaration was done, but in retrospect even he agreed that section 3 had been invoked.

So for about 8 hours on July 13th, 1985, George H. W. Bush was acting president, while Reagan was undergoing surgery.

And his son, George W. Bush, is the only president to explicitly invoke section 3, and he did it twice.
In 2002 he invoked it for a little over two hours for a colonoscopy, making Dick Cheney acting president.

He invoked it for another two hours, in 2007.

For a colonoscopy, again.

So yeah. The two times it was definitely invoked were for a colonoscopy, and the somewhat-debatable time was for a bowel cancer operation.

Not to mention the first serious consideration was for a hemorrhoid operation.

THE 25TH AMENDENMENT, SECTION 3:
LEGAL ISSUES REGARDING THE PRESIDENT'S BUTT

for completeness, sections 1 and 2:
1. when the president is removed, dies, or resigns: the vice president becomes president
2. whenever there's a vacancy for the vice president, the president nominates someone, and a majority of congress has to confirm them.

the combination of these two sections is how we got President Gerald Ford without anyone ever having voted for him.

because Nixon's Vice President Spiro Agnew resigned on October 10th 1973, and after being confirmed by congress, Gerald Ford became the new vice president on December 6th.

Then on August 9th, 1974, Richard Nixon resigned.
Section 1 was automatically invoked and Gerald Ford became President.

This inherently involved section 2 as well, though. Since Gerald Ford was now president, there was no vice-president.
So he nominated Nelson Rockefeller, who was confirmed in mid-December.

And that's all the times that the 25th amendment has been invoked! It was only ratified in 1967, which limits the number of times it could have been important.

One of the reasons it was proposed was the assassination of JFK in 1963. For example, if JFK had been put in a coma by the attempt, there would have been no way to have the vice president take over other than to impeach him.

And after JFK's assassination, the new president was someone who'd had a heart attack once already, and the next two people in line for the presidency were over 70.

So it raised the issue of maybe clarifying how the line of succession worked, letting a VP be replaced (prior to the 25th amendment, the office just stayed vacant until the next election), as well as issues of potential disability

as well as the obvious issues of...

THE PRESIDENT'S BUTT

BTW when I quoted the amendment I changed the pronouns. The amendment only uses "his", and it uses it nine times.
We're 8 days off from having a female vice president, so start your clocks until someone argues that the 25th amendment can't apply to her.

there is a loophole, though: section 2 (which allows the president to nominate a new vice president) doesn't use any gendered pronouns. Only the other 3 sections are all he/him.

so yeah, if you're having trouble remembering the 4 parts of the 25th amendment, just remember:

Sections 1-2: Gerald Ford
Sections 3-4: Butts