Perhaps that should be the title for the 2016 presidental (primaries) election. It's happening in both parties, and neither party is dealing with it particularly well.
On the Republican side we have Trump: an ignoramus with baby fingers on full sized palms who regularly lies and self aggrandizes whose only consistent platform is hating on [women, Hispanics, Muslims, Asians, blacks...]. The GOP has been stoking this resentment and hatred for decades, but the thing is that when they get into power they don't do as much about it as they brag, though they do shovel taxpayer dollars at rich people and the military very well. Their voters have gotten fed up with them and the past few congressional elections should have been fair warning, but they kept going down that path and now they get Trump.
The Democratic side is not quite so bad, but it does suffer from a mirror image problem. For quite some time now the more liberal people in this country have been, regularly, on the right side of many (most) issues, but have been told by the establishment that they are fanciful dreamers that don't understand how the world works and they should just let the people who know things handle the government. The liberals are now beginning to get pissed.
I like Bernie Sanders, though not so much for president, and I'm not much of a Clinton fan (really neither Bill nor Hillary) but think she would do a fine job as president. As such, the Democratic primary didn't do much for me. But some people are just bonkers about it, and I think I sorta understand why. It isn't that Bernie or Hillary is the greatest or that the other is a monster. Sanders fans are, by and large, the most ignored group within the Democratic/Dem-leaning block. They want higher taxes, more redistribution, less inequality, less war, and the Democrats we have elected these past 20ish years have all pretty much done the opposite. Unlike Republicans, though, who pander to their supporters, Democrats tend to patronize theirs, there's even a term for it: hippy punching.
When people get ignored repeatedly by those who are supposed to be representing them, they tend, over time to either get pissed or just drop out. Historically the ignored on the Democratic side have dropped out (to a greater extent than Republicans*), so Republicans typically win larger shares of the elections than they are shares of the electorate or the population at large (gerrymandering makes it worse, but the GOP is more likely to show up to vote anyway). Whether it's just normal societal trend or something that has been pushed thanks to the internet, this year more of the ignored liberals are pissed.
I'm not sure how this is going to manifest itself over time, but the Democratic establishment/leaders should probably be careful. There is some evidence they are, since even as people like Krugman continue a campaign to insult and isolate Sander's supporters, Clinton supporters who are also elected officials know better. On NPR they were interviewing [don't remember...McCaskill?] and she made a point of saying the energy and the people that Sanders was bringing into the campaign were good things, and she supports Clinton.
The direction of the Democratic party is toward Bernie Sanders. If the leaders of this party want to keep it from breaking up they need to really embrace the ideas behind it. Clinton will get the nod at the DNC. When she does, if she turns and runs and governs as GOP light as so many Democrats have been doing the past couple decades,then she is going to have to face a similar type of shit-storm to that which the GOP is seeing this year. The good news is that governing like the Democratic base wants would actually be popular (though not to Wall Street types), and without the racist/chauvinist problem to go with that the GOP has.
*Frightening note: one particular group of GOP-leaning people have dropped out and Trump actually seems to be getting them to the polls: white supremacists.