http://www.dsausa.org/pc/pc.members.html
Also, this link is to the "Progressive Agenda". (keep in mind, this is the dem socialists of America's web site). Sure sounds like socialism to me. You ask any lefty and they'll tell you that "progressive" is the code word nowadays for "socialist". It's just that simple. They change their name and suddenly they're invisible. But they're socialists, make no mistake about it.
Oh, I have no doubts, looking at the list. But it's foolish to make a claim that X is a member of Y if both X and Y can shoot you down by simply denying it. I suspect these critters are way too careful to call themselves socialists (except for Bernie Sanders, and they'll elect anything in Vermont as long as it's queer, er, I mean odd. ) 'Progressive' doesn't have the same connotations, even though it means the same thing.
Because the Congressional Progressive Caucus comprises the crypto-Marxists of Congress. Check out the names on the list! The good news: Komissars Hilliard and McKinney are on the way out, and Wellstone may be as well.