Article II, Section 1, Clause 6:
In Case of the Removal of the President from Office, or of his Death, Resignation, or Inability to discharge the Powers and Duties of the said Office, the Same shall devolve on the Vice President, and the Congress may by law provide for the Case of Removal, Death, Resignation or Inability, both of the President and Vice President, declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed, or a President shall be elected.
When the President is disabled or is removed or has died, to what does the Vice President succeed: to the
powers and duties of the said office, or to the office itself? There is a reasonable amount of evidence from the proceedings of the convention from which to conclude that the Framers intended the Vice President to remain Vice President and to exercise the powers of the President until, in the words of the final clause,
a President shall be elected. Nonetheless, when President Harrison died in 1841, Vice President Tyler, after initial hesitation, took the position that he was automatically President, 1 a precedent which has been followed subsequently and which is now permanently settled by section 1 of the Twenty-fifth Amendment. That Amendment also settles a number of other pressing questions with regard to presidential inability and succession.