Josh Marshall, writing at Talking Points Memo about why the Sanders campaign continues to attract so many rhetorical bomb-throwers:

Many have noted that ‘socialism’ is less an ideology for Sanders than a brand. Look at his voting record in the Congress and it’s little different from dozens of other left-liberal or even just liberal members. His real practice isn’t nearly as left as some of his supporters claim or his adversaries fear. As he himself often says, he calls it “democratic socialism” but really it’s mostly traditional labor-liberal New Dealism.

So that part of Sanders is pretty substantially different from the guy who was running with or for various fringe third parties in Vermont several decades ago. But the political gestalt, the political posture of the sectarian left hasn’t changed nearly as much. You see it in seemingly symbolic things like his continued refusal to join the party he professes to want to lead. That is what attracts these wrecking voices to his banner and makes him unwilling or uninterested in denouncing or trying to rein in their excesses.

You can actually see this contrast most with Warren. Their policy list is pretty similar. But backing Warren makes no requirement that you recant or apologize for supporting Obama or Clinton or any of the rest of the continuity of recent decades of the Democratic party. Her policies are a significant departure. But it’s just presented as a next step. The premise in the milieu around Sanders is that the stuff that happened before – Clinton, Obama, whoever else – was wrong. And you kind of need to admit that it was wrong. That may be true or not. But it’s a difficult sell to the mass of the Democratic party when Obama remains overwhelmingly popular.