Well, Vermont is not a microcosm of American, but I get your point. The socialism thing is a problem. It really, really is. We don't get to throw away decades worth of fear about it simply because Bernie thinks we should. As Cooper told him, the ads write themselves. They will come after him hard and fast on that issue should he get the nomination. He's said he's not a capitalist. He wants to be like Denmark. Hillary, at a Democratic debate no less, got to hit him over the head with "We're not Denmark." It got a round of applause. The GOP will destroy him over that and his vacation to the USSR. Is it stupid? Yes. Will it work? Yes. So far, Sanders defense has been "I'll explain it to them." He had a chance to do that at the debate and he, once again, punted on the issue.
Bernie's type of politicking works well in a small state. He's running a national campaign now. Not everyone is going to meet and fall in love with him. He needs to be far more targeting in how he deals with things and vulnerabilities. Of course, he doesn't run polls, so he doesn't really know where he has issues until they, quite literally, get into his face.
If he wins the nomination, yes, I assume that Obama would endorse him. The DNC would give him support, but, at a certain point, they'll have to do what's best to try and preserve the party. If it looks like he's going to get blown out, they'd probably want to target resources to down ballot races.
However, a party's candidate is supposed to be the leader of the party. Until 2015, Bernie Sanders was not a Democrat. He has no loyalty to the individuals who make up the party, and they have no loyalty to him. That's a problem. How can he lead the party when he's not been there taking the lumps with us? It's an image problem, and he's never really addressed it.