The 25th Amendment to the US Constitution, initiated by Congress in 1965 and ratified by 3/4s of the states in 1967, has four parts. I expect that the part that people are posting about online is referring to the fourth.
Briefly, the other three. Section. 1. In case of the removal of the President from office or of his death or resignation, the Vice President shall become President.
This is alluded to in Amendments 12 and 20 but is much clearer here. JFK’s assassination in 1963 was surely on the minds of the citizenry.
Section 2. “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.”
Gerald Ford (under Nixon) and Nelson Rockefeller (under Ford) became Veep under this provision.
Section 3. “Whenever the President transmits to [Congress] 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.”
The 25th Amendment has been used 3 times to relieve presidents deemed unfit to govern — each case involving physical health.
Section 4, as noted, is the item most discussed. As early as May 2017, the question was whether the vice president, Cabinet, and Congress would determine that the current White House resident was “unable to discharge the powers and duties of his office.”
It is not easy, but it is convoluted. “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 [let’s say the Cabinet], 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.
“But when the President transmits to the [Congressional leaders] his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and [the Cabinet] transmit within four days to the {Congressional leaders] their written declaration that the President is unable to discharge the powers and duties of his office.”
Then “Congress shall decide the issue… [if by a] two-thirds vote of both Houses [determine] 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.”
One can argue that the removal SHOULD happen. It won’t. I have serious doubts that, even if the House voted to impeach, the Senate would vote to convict. Ultimately, the only solution is the ballot.