Being a Democrat doesn't automatically mean that what you do is right.  And I don't think the animosity has ever been hidden.

Yes, he was heading the DCCC for this election, but it does not automatically hold that he is RESPONSIBLE for that.  You're probably wearing a shirt right now, and if you flap your arms, you won't be able to fly.  Just because both facts are coexisting does not mean that the one impacts the other necessarily.