This is a very good question. Remember that the democrats used to hold power with well-disciplined blocks of votes from interest groups like big labor. However, that has broken down to a great extent.
1) Are big unions still being allowed to "cheat" in elections, using their personnel to support democrat political campaigns?
2) Other interest groups like the NRA have been suspiciously quiet this election cycle. Could this harm the republicans?
3) Will outright cheating and malfeasance, like in King County WA, be decisive; and how many races will be contested in the courts?
4) How great is the republican "gerrymander" advantage based on redistricting?
5) Are there to be any more last minute October or November surprises?
I don't have answers for 2, 3, and 5, but I'm going to write a bit about 1 and 4.
From what I hear, at the plants, Dems are allowed to put out their material because the union says that it's UAW sponsored. And usually, they get the day off, "to vote".
However, a lot of R supporters are in the unions, but they have to keep quiet about it because they don't want to mess up their union status. I've had different people come up to me and say that their whole department is voting R. And because Labor is a huge in MI, we've learned how to get our message out more effectively.
As for the districts here in MI, there isn't a close race for the House that we have to worry about. And the big focus is on the Senate and knocking out Stabenow, so that would be a gain for the R's. There are Congressional races that the lefties are trying to target, but I don't think that they are going to pull off an upset.
I really don't think the Dems on my state are as motivated as the Republicans. When it comes right down to it, it's very anti-incumbent out there - and our current governor and Senators are Dems - so I think that their victory dance is really premature here.