Some of these scenarios have virtually no chance of happening, particularly the ones where Democrats play even in the Senate or even gain a seat. The Democrats have only a couple real chances to play offense, and their odds in either case are not great.Professor Sabato sees a wave coming, and I've come learned to listen to his political prognostications. Go read the whole thing at the link. It's great reading.
And you can see his regular blog at Sabato's Crystal Ball.