So I had asked myself "Who is Captain America?", and had found an answer for the man. Thing was, America was moving from the overarching Vietnam War toward the specific crimes of Watergate.
I was writing a man who believed in America's highest ideals at a time when America's President was a crook. I could not ignore that. And so, in the Marvel Universe, which so closely resembled our own, Cap followed a criminal conspiracy into the White House and saw the President commit suicide.-Captain America writer Steve Englehart
Cap didn't tell anybody, even the Falcon, what happened in the White House, and "the authorities put a lid on it, too." Does that mean Nick Fury had a Life Model Decoy running the country (at least until they could engineer Nixon's resignation)? And yes, that was intended to be Nixon, though we never saw his face. Steve Englehart, the writer of the book, explained:
People often ask if Marvel hassled me for the political vibe in this series and others, and the honest answer is that they almost never did. It was a wonderful place to be creative. Here, I intended to say the President was Nixon, but wasn't sure if Marvel would allow it and so censored myself - probably unnecessarily.