"Cap for President!"
Micro-comic published in 1987, reprinting the story originally in Captain America (1968) #250, October 1980.
Rescuing politicians from a terrorist attack brings Cap to the attention of a small political party who wants him to run for President. Cap thinks about it, but finds that his political party has jumped the gun and announced that he is now a Presidential candidate. After some soul-searching, Cap holds a press conference to announce that he cannot run for President.