Donald Trump is on the verge of a stunning victory in the 2016 election, confounding pundits and forecasters by winning states where he rarely or never led in the polls.

The explanation for this increasingly probable outcome is pretty simple. Trump has won white working-class voters who used to vote for Democrats, and by margins that appear to be destroying the “firewall” that was meant to assure Hillary Clinton’s victory in traditionally Democratic states.

Those voters used to be fairly split between the parties. But as the New York Times’s Nate Cohn writes, this year white voters, particularly white voters without a college degree, formed a voting bloc around what they saw as their shared interests:

How to think about this election: white working class voters just decided to vote like a minority group. They're >40% of the electorate. — Nate Cohn (@Nate_Cohn) November 9, 2016

That’s how Trump’s campaign — which embraced overt white nationalism to a degree unprecedented in recent American politics — was able to beat the odds and come, now, very close to victory.

Watch: What the media gets wrong about Trump voters