How many presidents have become president because they were vice president at the time of their presidents' incapacitation?

Answer 1

Nine vice presidents have taken office as president after the incapacitation of the previous president. Eight of them came to office following the death of the president, and one, Gerald Ford, became president following the one presidential resignation [Richard Nixon] in US history to date. See links for details.

When Nixon's vice president Spiro Agnew resigned, Gerald Ford was appointed vice president according to Constitutional provisions. When Nixon later resigned, Ford became the only president so far who was never elected to the presidency OR to the vice presidency. In essence, he was an appointed, not elected, president.

We in the US are fortunate that provisions were already in place to handle the unusual circumstances involved in the Nixon resignation. Less involved transitions have caused turmoil in other countries. Having an orderly and reasonable system for the transfer of power is an essential element in modern democracies. You can look to several currently unfolding transitions for evidence of this.

Answer 2

Only one US president has ever resigned and that was Richard Nixon in 1974. Vice president Gerald Ford became President because of his resignation.