I think Sanders has managed to poison his own well. Plenty of Democrat voters hate him for spoiling the 2016 election (whether or to what extent he can reasonably be blamed for that is irrelevant; the minority of voters who are willing to try to evaluate candidates rationally is too small to have much effect). Plenty of others dislike him for failing to rein in his more offensive supporters, or for one or more policy positions, or for some other sin.
He's too thoroughly inscribed to be a viable US candidate at this point, unless he can achieve the level of demagoguery Trump has - and I don't see him doing that. To be honest, I don't see any Democrat candidate winning using Trump's approach. The Democratic Party had masters of populism a century ago, but they let that set of tactics fall fallow.1 Meanwhile, Republicans and Republican sympathizers took them up starting around the time of Carter's election in the '70s, after seeing that in a post-Nixon era the electorate was no longer keen on stiff managerial types. They've dominated a number of media - talk radio, pop policy books - since, and at least achieved a draw in a number of cultural conflicts since.
These days Democrat culture icons generally have to try to occupy the moral high ground - a precipitous position. It's a lot easier to win over your audience shouting from the gutter than it is preaching from the pulpit.
1Not that I think that's a bad thing. Appealing to the baser instincts often succeeds, but there's a limit to the realpolitik I'm going to endorse.
Biting the hand that feeds IT
