This thread illustrates one of the real challenges of the democratic systems. That being, we tend to vote emotionally rather than rationally. But confabulate justifications for our emotion-based behavior to pretend they are rational, making it unlikely we'll take a step back to reassess.
One thing I think many Bernie supporters forget is that while he caucused with the Democrats in the Senate he deliberately positioned himself as an outsider to the party itself, and at odds with it's core. While the primary has helped highlight that younger voters, and the future of the democratic party, are probably closer to Sanders than they are the current party center, the primary seasons of a Presidential election are never about the center. The election is about to shift away from him, even if he were the nominee. Regarding the next 5 months, most Americans could probably already distill the marketing about both likely nominees: Trump is arrogant, bigoted, and under-qualified. Hillary is untrustworthy. The general election is going to be those two messages turned up to 13.
ETA: If the election were a hand of poker, having Trump be the nominee for the Republican party is like having a wild card face up in the community cards. There are few certainties at that point. Even still, I have to imagine that many Americans would have a far harder time with Sanders than seems to be the feeling among those who support him. Clinton needs Sanders supporters and the Democratic primary was very tame comparatively speaking. Running ads about Bernie's vision for bigger government and social programs with photos of Sanders cavorting in Soviet Russia like this? -

- not sure how that would have played in Peoria.