So, he’s conceded he knows he can’t win, so going to vote with the party in hopes of some sort of reward after he’s ejected this fall..
The DNC isn’t going to waste funds on him.
That's exactly it. He knows he's going to lose his Senate seat this November no matter which way he votes. To ensure his future as a democratic operative he's got to stay in the good graces of the party leaders, that's all this vote is about. If he votes to acquit then he loses the election and he's made himself a pariah in the democratic party. If he votes guilty he still loses the election but he remains in good standing with the commies.