Evidence of the collapse in the middle is the lack of support for everyone in the middle. Hillary, JEB, Boehner. Democrats went to Bernie. Republicans went to tump (for the most part) Some stayed in the middle. I felt, as example, - better to support Hillary on the left of the tug-o-war; Bernie didn't have as good a chance to win. Republicans felt, that though they were actually closer to HRC and didn't like tump, at least he was party, and better to support him than to cross the line, and lose the tug-o-war.
If the left emerges winner, there will be plenty of RINOs, and If the right wins, there will be lots of DINOs. Candidates who wish to run against incumbents, in solidly blue, or red districts will run as the opposition, to gain some party support, and name brand recognition.