The Republican insurgents have a pretty good shot, because the GOP's been encouraging demagoguery for some time... and perhaps more importantly, pretty much lying to their base. "We can totally do this with what we have!" *Gets elected, spends no effort on that*. "We totally must stop this or everything will explode!" *Doesn't stop that because they, obviously, didn't have the votes for it. Things don't explode. Makes the same promise/claim next time*. It's no surprise they aren't trusted.
The Democrats, less-so. Obama did what he was elected for, less than desired, but he without a doubt tried. The Democratic party does not feel betrayed. Heck, Bernie isn't so much getting support on being anti-establishment, so much as being pro-things like free college and heavier socialist policies that'd help workers.
They could beat a Hilary/Castro ticket.Between Trump and Sanders, they could find common sense regulations, make Trade Deals pro America, increase jobs by producing them here, and save Social Security and take care of veterans.
I do believe so many Sanders people would quit-out if he joined with Trump. I mean, over 60% of Sanders voters say they'd be satisfied with Hillary, 77% say they would vote for her. Join with someone who wants to build a wall and start a trade war with Mexico- remember Bernie is *not* anti-immigrant- and supports a conservative tax plan very much at odds with Bernie's high taxes for the wealthy? Unlikely, to say the least.
Also: Trade Protectionism is not 'pro-America.' A lot less trade means a lot less money. That's one of the big causes of the great depression, when the economy took a hit everyone was like, "We'll keep our jobs at home!", cut off trade, and poof, a lot of jobs just vanished.