This was my first real story arc featuring Cap. It's about five issues long, but as is my want, I bought the final issue here first and then found the other ones. The gist of the plot is that one disgruntled person is upset that Nixon is reaching out to the Red Chinese and releases the Captain America and Bucky who were active in the 50s . These two had also taken the Super Soldier serum, but didn't have the necessary Vita-Rays to make their minds stable. Consequently they became paranoid, seeing commies everywhere, especially in areas where minorities lived. They refused an exposure to the Vita Rays and were subsequently put on ice. There's much more to this backstory, but that's all that was reported in this storyline back then, thanks retconning. Suddenly they are free with a "new" Cap who isn't as tough on the Reds and also has a best friend who is black. Naturally there's confusion abounding with two Captain Americas running around, not to mention Bucky being alive...
This is all wrapped up in this final issue so well, as written by Steve Englehart and drawn by Sal Buscema. It's what my idea of Cap should be, strong and compassionate. He didn't try to kill his ultimate fan, just stop him. He was tortured by the fact this man wanted to be just like him, but took his patriotism to the nth level and it let his bigotry run wild. He still does his job and stops him. The mirror image is always the hardest foe to fight.
Marvel has revisited this story several times since then, in What If...? issues as well as newer ones. Having not read many comics since 2002 I'm not exactly sure what Cap 4 has all gone through, but I'm sure it's been a lot.
I like this Cap from the movies, though I wish he was less a soldier. And he's still not the first Avenger.