I think that's an unfortunate misunderstanding of Trump's base, and one that Clinton made as well with her "basket of deplorables" comment. Dismissing them as hopeless, inveterate xenophobes that cannot be appealed to by any means is how we lose this race. Certainly, the xenophobes all vote for Trump. But not all Trump voters are xenophobes.
Well, no, there are also people who show up and vote party line, and people who actually think that he was a successful businessman as well. I don't see how Bernie the Socialist would win over either group - one simply won't listen, and the other plainly prefer capitalism.
Genuine question - how was Clinton planning to win over these people? She and Bill were already centrist Dems, so short of her planning to make appearances in her Reagan '84 T shirt (which Bernie somehow prevented) were you under the impression that she picked up any voters from either group?
With all the prognostication happening here, I'm sort of reminded of the last election where so many Dems were convinced the Fundagelicals hated Trump, but... well the rest is history. And as a matter of historical accuracy - considering Clinton being a right-wing-radio chew toy for the better part of the last 30 years, do you either group actually was less likely to vote Trump with Clinton running rather Sanders? And at this point, Clinton talk is blasé. Do you think those groups will really be more likely to vote for any of the Democratic field than Sanders? The way I hear the argument, it's that Sanders has so many things that are objectionable to many groups of people - but from a strategic perspective it doesn't matter how many different reasons someone has for finding you objectionable. See, the thing about people who think Sanders is a socialist NY Jew who consorts with sodomites and baby-killers is that they thought the same about Clinton, and they do about anyone with a (D) next to their name. Which is to say, attrition won't really be a big driver in this election, because anyone who is strongly for either parties' planks is pretty committed to the party - namely because both parties have effectively optimized for those factors.
The one factor that, unlike guns or abortion or the environment or sex education or queer rights or minority rights or education or immigration or health care, isn't sorted along party lines is income. See the thing is that while Dems have much stronger support in the bottom of the distribution, it just barely skews higher for Reps at the top of the curve
https://www.statista.com/statistics/940427/2018-midterm-election-exit-polls-votes-by-income/ and moreover, voter participation is much higher at the top of the curve. But the thing is that, while the rich Ds tend to the Capitalist faction, and the Rs Industrialist, neither group is really an antipodal political force, nor could really expect to get much crossover voting from the other side. Wealthy NY liberals will not be voting for Trump, mainly on the basis of all those other issues, should Sander get the nomination. Nor the wealthy Georgian Reps for Biden or Buttigieg or Warren.
The real strategic question is would a Sanders run could suppress the votes of wealthy liberals, and could it pick up the votes of non-voting non-conservatives, and what the relative value of each vote is. Frankly, wealthy liberal votes aren't particularly valuable because they tend to live in places which could absorb a reduction in turnout but they don't tend to live in battleground states. This is where Sanders actually has the most opportunity - represents VT, isn't an Ivy League dickhead, doesn't have a Wall St background, isn't a lawyer, and doesn't seem focus grouped. Anyone else in the Dems' field will simply be a repeat of last election, even if they technically have higher appeal to the anti-Socialist anti-Semite demographic.
It ain't 1992 anymore, and the New Democrats ain't new. Reaganomics is dead and the Reagan wave has receded to the abyssal depths of the Republican party. I think a large part of Obama's appeal was the amount of FUD the Republicans created and his freshness on the field - contemporary billing being that he was the most liberalist candidate to ever liberalize.