who was the prez who took over from Palmer when the faction said Palmer was incapacitated ciz he hesitated about going to war in response to the nuke bomb? That's who I thought you meant.
Palmer resigns from the Presidential race at the end of Season 3 and Keeler wins the election that occurs after Season 3.
Keeler is on Air Force One and it is show down in Season 4. Keeler is in a coma (he is really dead but Fox wouldn't allow them to kill a sitting President on screen) so Logan is sworn in as President.