It recently occurred to me that I've seen this before.
Hillary's "basket of deplorables" comment is enlightening.
First of all, calling everyone who opposes you ignorant racists is the same failed strategy that the anti-Brexit people used.

Because of how generally satisfied they are with their lot, they regard with affection and respect the internationalist institutions that safeguard the West’s prevailing order: the World Bank and IMF, NATO and the West’s military forces, the Federal Reserve, Wall Street, the EU. While they express some piecemeal criticisms of each, they literally cannot comprehend how anyone would be fundamentally disillusioned by and angry with these institutions, let alone want to break from them. They are far removed from the suffering that causes those anti-establishment sentiments. So they search and search in vain for some rationale that could explain something like Brexit — or the establishment-condemning movements on the right and left — and can find only one way to process it: These people are not motivated by any legitimate grievances or economic suffering, but instead they are just broken, ungrateful, immoral, hateful, racist, and ignorant.

That's not to say that xenophobia wasn't a significant part of the Brexit movement (it was), and that it isn't a significant part of Trump's supporters (it is), but making it all about that is intellectually dishonest.

It reminds me of how Republicans disregarded the huge anti-war demonstrations before the invasion of Iraq because a minority of the protesters were radical socialists. Like liberals today, they didn't want to even consider that the other side might have legitimate grievances, so they looked for an excuse to dismiss them, and if you want to look hard enough you'll find one.

We know for a fact that most pro-Brexit voters didn't vote that way for reasons of racism, but the liberal elite doesn't want to hear it.
Instead, the liberal establishment has a hissy fit.

CNN's Christiane Amanpour linked the vote to xenophobia five times during her Brexit coverage late Thursday evening and early Friday morning.
"We must learn from brexit: Elderly xenophobes will lie to pollsters to hide their racist views, then vote for destructive policies anyway," said blogger Anil Dash.

Which just shows that the liberal elite aren't prepared to learn anything.

Consider this South Park episode.

Even I think it's kind of funny. However, the subject isn't funny at all.
If you lose your job to immigrants because they will work for peanuts, that's a big deal. You have a right to be pissed.
Pointing fingers and laughing at the poor slobs who lost their jobs is pure elitism.

One thing that Christiane Amanpour and the liberal establishment should have learned from Brexit is that a news media united in condemnation and ridicule of a segment of society doesn't achieve anything but harden their resistance as long as their grievances are real.
It didn't work with Brexit, and it's not working against Trump supporters.

You interviewed Chris [Hayes] about Brexit and I just want to submit to you that the mistake the U.K. media and U.K. elites made with Brexit is the exact same one that the U.S. media and U.S. elites are making about Trump. U.K. elites were uniform, uniform, in their contempt for the Brexit case, other than the right-wing Murdochian tabloids. They all sat on Twitter all day long, from the left to the right, and all reinforced each other about how smart and how sophisticated they were in scorning and [being snide] about UKIP and Boris Johnson and all of the Brexit leaders, and they were convinced that they had made their case. Everyone they were talking to—which is themselves—agreed with them. It was constant reinforcement, and anyone who raised even a peep of dissent or questioned the claims they were making was instantly castigated as somebody who was endangering the future of the U.K. because they were endorsing—or at least impeding—the effort to stop Brexit. This is what’s happening now.
Do you think the people voting for Donald Trump because they feel their economic future has been destroyed, or because they are racist, or because they feel fear of immigrants and hate the U.S. elite structure and want Trump to go and blow it up, give the slightest shit about Ukraine, that Trump is some kind of agent of Putin? They don’t! Just like the Brexit supporters. The U.K. media tried the same thing, telling the Brexit advocates that they were playing into Putin’s hands, that Putin wanted the U.K. out of the EU to weaken both. They didn’t care about that. That didn’t drive them. Nobody who listened to Trump could think that was genuinely a treasonous request for the Russians to go and cyberattack the U.S. government.

I don't want a President Trump. I think he'd be a horrific president.
But unless the liberal establishment learns just a tiny bit of humility, and how to listen to people they don't agree with rather than just judge them, that is exactly what is going to happen.