I'm very excited about the prospect of Feingold returning to the Senate, and it looks like the GOP is just giving up the seat which is great. Feingold, Warren (if she's not VP), Sanders, Franken, Brown among several others working on liberal legislation together... Man. I think progressives will have a remarkably effective operation going on there.
In fact, let's look at the Senate battleground.
Democrats just need to make sure they hold down Nevada, which is very likely if Trump is getting blown out at the top of the ticket. Masto's a great candidate in her own right and she's got the Reid machine working for her. Wisconsin, Illinois and Indiana are all gimmes, so that puts them at 49 already, one seat away from a tie/majority.
New Hampshire, Florida, Pennsylvania, Ohio, North Carolina, Arizona and Missouri (in that order probably) all have incumbents mired in the low 40s and very strong challengers. In a wave, it can be expected that these would all fall over at the same time like dominoes (although I would put a line between those first four and the rest - it'll take a great year to dislodge Burr, McCain and Blunt, although I think we're looking at one).
Going into 2017 with 56 Senate seats? Oh man. Not to mention that in waves, races tend to develop where they shouldn't be developing. Not saying it'll happen, but one can envision a scenario where suddenly Chuck Grassley looks very vulnerable (he's already polling much worse than usual, even if that still gives him a somewhat comfortable lead). Remember that in 06/08, Democrats were very skeptical about their chances, but many races broke late including some that were never on anyone's radar.
