The real reason is that Webb HAS to run as a Rat, because he comes with baggage that means he could never run as a Republican ... so he joined the party of Willie Jeff, a/k/a Cold Hard Case a/k/a Dollah Bill; Tom Dodd, a/k/a Censure? The Idiots in KonneKtiKut Will Just Reelect me; Adam Clayton Powell, the Congressman from Bimini; Bobby "Big Bird" Byrd, a/k/a the Grand Wizard of the KKK, etc. He seems to fit right in with that crowd.
He and Sestak seem to be cut from the same jib. If given the chance they will expose their inner Howard Dean. Both have widely known reputations for their tempers. A heckler, or former peer giving some less than flattering information, will bring it out. Guaranteed.