Eve, on the question of which Democratic nominee would be better for House candidates, this is what National Republican Congressional Committee Chairman Tom Cole had to say in Sunday's New York Times magazine:

Cole has been giving that race a lot of thought. “I happen to think Hillary Clinton is a stronger candidate in the end,” he told me. “You couldn’t raise money against Obama right away like you could with Clinton, that’s true, and so maybe by the time you were able to raise money it wouldn’t matter. But he’s ideologically well to the left of Hillary Clinton, for all his rhetorical gifts, and I also think he’s got a national-security deficit. I think she’s a plausible commander in chief, and I don’t think he is. It may not matter. But those two areas are where we would fight the election, and with McCain, I think we contrast with him very well.”

Reverse psychology? Could be, although the piece made Cole sound like a fairly straight shooter overall.

Update: Okay, he's not actually talking about coattails per se. In my mind I sort of conflated this passage with the next, where he talks about areas where McCain could help GOP candidates:

On the Congressional level, Cole says that he believes that this election will be contested across a map just about as broad as the last one, with at least 75 seats in play, and that McCain contributes to opening up that map. “Let’s break it down,” he said. “Obviously in the Southwest, he’s going to make us much stronger. In Arizona, we have a couple of opportunities where he’ll help us, but also in New Mexico. Frankly, while some people have problems with his stand on immigration, he probably keeps Hispanics in play at the presidential level in a way no one else could. He really helps us in the Northeast and upper Midwest — Illinois and Pennsylvania. Then, anywhere where there’s a veterans population or military bases. Think of Jim Marshall’s seat in Georgia. That’s a huge advantage for us. Florida, big military presence. We have a couple of opportunities in Texas. But I think the biggest thing is he’s seen as an authentic American hero, someone who can take on and shake up Washington.” 

--Michael Crowley