The crowds at Clark's events also seem to skew further left than I expected. Recently he's campaigned with Michael Moore and received the endorsement of George McGovern. I think two things explain this. One, as a newcomer to the party, he overestimates how liberal Democrats really are. He still has a slightly caricatured view of his new home, and so he doesn't realize how silly he sounds when he calls Michael Moore "a great American leader," as he did in the debate. The other reason is more straightforward. He's still being attacked for voting for Republicans and praising George W. Bush, and so he's constantly having to demonstrate his liberal credentials.
Newcomerishness is an especially damaging problem when your campaign is premised on depth of experience.