When the president is meaning he is incapable of fulfilling his duties, the vice president assumes the office of the president.

Disabled/Incapacitated

When the president, for some reason, is considered incapacitated, the vice president takes over. This is because of the president-elect's removal. This is rare, but it is feasible because it is written in the Constitution. The president can be removed because of health problems, death or an impeachment process. However, for Impeachment to occur, the President must have committed some crime.

where is the passage