The 25th Amendment – A User’s Guide
The 25th Amendment of the US Constitution contains a provision wherein the Vice-President can assume the duties of the President if the Vice-President deems the President incapable of carrying out the duties of office. The Constitutional provision designates a “majority of the executive officers” (the Cabinet) as those who must agree with the Vice-President. The constitutional clause then passes the matter to Congress to write a statute to carry out that action.
That statute is 3 US Code Section 19, the Presidential Succession Act.
The current version of the Act lists the Cabinet officer who are in line for succession to the presidency, via a majority of them agreeing with the Vice-President, can support the Vice-President in taking over the duties of President. Those designated Cabinet officers are:
• Secretary of State
• Secretary of the Treasury,
• Secretary of Defense,
• Attorney General,
• Secretary of the Interior,
• Secretary of Agriculture,
• Secretary of Commerce,
• Secretary of Labor,
• Secretary of Health and Human Services,
• Secretary of Housing and Urban Development,
• Secretary of Transportation,
• Secretary of Energy,
• Secretary of Education,
• Secretary of Veterans Affairs,
• Secretary of Homeland Security.
However, only persons in these offices who have been appointed and have been confirmed in office by the US Senate are eligible to form the majority. Given the number of vacancies Trump has in his Cabinet, this might seem to be a problem, but the Constitution says a “Majority” can act, so that would be a majority of the officers eligible, excluding “Acting” Secretaries.
So, The Vice-President needs to get the support of a majority of the above list of cabinet officers behind him and file notice with Senator Grassley (Senate President Pro-Tem) and Speaker Nancy Pelosi and upon that notice the Vice-President takes over the duties as President.
There is a provision whereby Congress could act to support or oppose this action and to hear an appeal by the President. However, that would probably not occur in the next fourteen days.
That is how Vice-President Pence can remove Donald Trump from office.
There are lots of other details, but that covers the basics.