US Agent is like the version of Captain America the way people who don't like America think Captain America should act. Essentially he's like every 80s stereotype of Americans with super powers. He hates Commies, loves America, and actually has American Rage against his percieved enemies of America. Before he tried to be the new Captain America, he called himself Super Patriot.
They kind of made him look like Bill O'Reilly, and I got to say, I sort of think they're personalities are similar. The difference: US Agent isn't as perverted as O'Reilly. And say what you will about O'Reilly and US Agent, they both love America.