Thomas Lifson over at American Thinker notes the existence of documentary evidence that Barack was a member of the New Party -- that is, a group that was designed to offer more leftist alternatives to Democrats, and, presumably, push the party to the left..

Wikipedia describes the "New Party" as "social democratic" in orientation -- which is Europe-speak for Socialist.

More from Politically Drunk here and Red State's Erick Ericson here at Human Events.

It strikes me that if the New Party had just endorsed Barack, that wouldn't mean all that much; as Ronald Reagan put it, endorsements mean a group supports him, it doesn't necessarily mean that he supports them.  But membership in a group -- or running on its party line -- is something else again.