The Vice President's role as next in line for the presidency was officially
established by the 25th Amendment to the Constitution
Explanation:
In layman's terms, the 25th Amendment (Amendment XXV) to the United Constitution has to do with all matters as long as it's related to presidential succession and disability.
The Amendment points to the summary in quote; "whenever the President lacks the capacity to do their job, the Vice President steps up to become the President."
But this is only when the President is sick and/or disabled for a short period of time.
