I don't think Romney is as weak of a candidate that you think he is. I also tend to ignore those who believe that the Tea Party somehow controls the Republican Party. The Tea Party doesn't control shit, and to be honest doesn't really exist. Did some of the more conservative candidates win primaries? Sure, but I actually think the finger needs to be pointed at the more mainstream candidates that were beat, not the candidates that won.
I believe Romney is going to win on Tuesday, and there is a small part of me that thinks we wins big. That would mean he wins Ohio and other states like Colorado, Iowa, and Wisconsin. I have a hard time seeing that happen, but there is an opportunity.
As for the US Senate, I think Republicans make gains, but fail to get to total control. I actually see a 50/50 Senate split. Holing GOP Seats in Maine and Mass were always going to be difficult. Winning seats in Penn and Conn are never easy. Winning a Senate race in Florida and Ohio in a presidential year is never easy. There is so much money being spent in those states it makes it difficult to control your own race.
I actually expect to see a lot of split ticket results, where the one party carries the state for the presidential race, and the other party wins the senate seat. If this was a wave election that would be rare. I think we are going to see that a lot on Tuesday night.