Since white voters usually vote for the Republican, the difference on Election Day comes down to two things: How heavy that support is, and how heavily nonwhite voters turn out. With the advent of Trump as his party's nominee, many wondered how his presence on the ballot would effect the second part of that equation. His comments about Mexican and Muslim migrants offered natural reasons to assume that he'd fare much worse with nonwhite voters, just as whites were set to become an even smaller part of the electorate.
As it turns out, though, the biggest deviations in support from past nominees — particularly Mitt Romney in 2012 — aren't among nonwhites. They're among white voters.
We can compare margins from that Post-ABC poll (and one from NBC News and the Wall Street Journal) to demonstrate how it's shifts among white voters that have Trump trailing. (The bars below all show two-way matchups.)
In 2012, Romney won whites by 20 points. Trump's only leading by 14, as noted above — thanks to Clinton doing two points better now than President Obama did, according to exit polls, and Trump doing four points worse than Romney. Part of that is white men being much less supportive of Trump than Romney, with Clinton doing eight points better than Obama and Trump eight points worse than the last Republican nominee. White men are a key reason that Republicans always win the white vote. White women have voted for the Democrat twice since 1972, both times for Bill Clinton. (Well, 1992 was a tie, but you get the point.) White men have always backed the Republican.
The critical shift there is among whites with college degrees. This is a group that has also voted Republican in every election since Dwight Eisenhower was reelected. But thanks to a 28-point swing with that group (including Trump doing 15 points worse than Romney), Clinton is poised to be the first Democrat to win college-educated whites in a long time.
The margins among black and Hispanic voters are more subtle. Hispanics are nine points more likely to prefer the Democrat now than they were four years ago, according to that NBC-Journal poll, but that's more a function of Trump doing much worse than Clinton doing better. (A lot of Hispanics aren't committed to either candidate.) Black voters are heavily supportive of Clinton, which isn't a shock.
There are margins of error within these demographic groups that can result in larger apparent differences than exist in reality. (This is also, in part, why the margin between Trump and Clinton overall is only four points.) But these results comport with what we've seen from the campaign. College-educated voters are skeptical about Trump's candidacy for the reasons we expected nonwhites to be hostile to him: His views on immigration and racial politics. This is apparently why the new Trump team that stepped in to run the show in mid-August put a focus on targeting nonwhite voters, hoping that the outreach would convince white voters that he wasn't biased.
But most Americans say Trump is biased against women and minorities — meaning, if that strategy worked at all, it doesn't seem to have lasted. So the results three weeks from now will probably come down to an unexpected question: Can Donald Trump perform as well with white voters as Mitt Romney did?
The answer so far is no.