Hi there. The 25th amendment, ratified in 1967, deals with presidential succession in case the President dies or is removed or otherwise becomes unable to carry out the duties of the office. It’s a long amendment, as amendments go, and it has lots of interesting stuff in it. Section 4 is my favorite part–it says that the Vice President along with a majority of principal officers of the executive departments can basically declare that the President is unable to discharge the duties of the office, in which case the VP immediately assumes the duties of the office as “Acting President” unless the President disagrees, in which case the President gets to resume his duties, unless the objectors send a notice to Congress within four days that the President actually really and truly can’t discharge the duties of the office, in which case Congress gets to decide who gets to carry out the duties of the President–the President or the Vice President.
Anyway I came across this long, new scholarly article on the the Amendment yesterday. Maybe you’d like to take a look at it.