This is especially interesting because Trump may have the potential to pull a non-trivial number of swing voters in Rustbelt states like Ohio and Michigan with his (superficial and demagogic) criticism of "trade" treaties.
Erik Loomis is unimpressed with this position, as he explains in Did Hillary Clinton Defeat Bernie Sanders on Trade? LGM 03/20/2016:
The trade issue has been central to the entire Bernie Sanders phenomenon. Hillary Clinton might defeat that phenomenon. She almost certainly will, thanks to her structural advantages, his late campaign start, and his inability to reach parts of the Democratic base on issues other than trade and the economy. But this hardly means it’s time for Third Way hacks to pat themselves on the back and start working for a Grand Bargain with Republicans that will gut the social safety net in exchange for circus peanuts. If these people are smart, a point very much in doubt, they will realize that the left-wing rebellion within the Democratic Party on trade, the minimum wage, and economic inequality, has likely only just begun. There will be continued demands for a higher minimum wage (which I believe would be a very early priority of President Hillary Clinton), for trade deals that help American workers instead of export their jobs overseas, and for broad-based measures to reduce income inequality. Hillary Clinton didn’t win North Carolina and Florida or Ohio because voters thought she was right about trade. She won for entirely legitimate reasons, but not because the Democratic base really believes in this supposedly nuanced but what is rather a political opportunist position on trade.And he notes, "It’s something to take seriously because large swaths of the Democratic base are demanding action on these issues more than they have in a half-century."
Ruth Conniff's Just How Scary Is Donald Trump? The Progressive 03/18/2016 addresses the potential appeal of Trump in the general election. She interviews Political Research Associates Director Tarso Luís Ramos:
I caught up with Ramos by phone recently, to talk about Trump’s appeal, what the left gets wrong about him, and why Ramos thinks he could win not just the nomination but the general election.
“Is there potentially a mass base for Trump’s brand of bigoted nationalism? I would say yes, absolutely,” Ramos says. “Many think Trump could not prevail in a general election. I’m not convinced,” he added.
Trump’s campaign has been a magnet for organized white supremacist groups, which have been actively recruiting members at his rallies. But more importantly, Trump is attracting large numbers of new voters with a classic rightwing populist message.
While Trump himself does not come out of the white nationalist movement, from the David Duke point of view, Trump is helping the cause by broadening the constituency for white nationalism, and allowing hardcore white nationalist organizers to “reimagine” the possibilities for themselves. ...
Trump appeals to the losers from decades of pro-corporate, race-to-the-bottom economic policy, austerity and privatization.
The Democratic Party helped pave the way for him, by abandoning its role defending Main Street against Wall Street.
“We have two neoliberal parties with some significant differences but far too little on offer for the majority in economic terms. It’s a very explosive contest,” says Ramos. “The rage is real, and it’s not clear that establishment neoliberal politics can trump it.”
If Bernie Sanders is not in the race, the sharpest economic populism on offer in November will likely be coming from Trump.
Paul Waldman also takes it on in How to Explain Which Republicans Will Support Trump, and Which Won't The American Prospect 03/21/2016. He focuses particularly on the high likelihood that the Republican Party will fall in line with Trump as the nominee:
[Republican] politicians have almost nothing to gain by categorically opposing Trump. A pundit can say whatever he wants—even endorse a third-party candidacy that would retain some kind of ideological purity while it delivers the White House to Hillary Clinton — and keep his job. It may even benefit him, since he can look principled and brave. But politicians don't have that liberty.
That also means that if and when Trump does win the nomination, almost all Republican politicians—with the possible exception of those representing swing districts and states—will rally around him. They may not feel good about it, and they may worry about how it will make them look. But it will be the only thing that's in their interests.