Matt McDermott of Whitman Insight Strategies picked out the most remarkable shift over that time period. White women with college degrees were about evenly split between Romney and Obama in June 2012, according to Pew's numbers. Now, Clinton leads Trump by 31 points.

That's by far the biggest change since 2012, but it's by no means the only one. In most cases, demographic groups look more favorably at Clinton relative to Trump than they did at Obama relative to Romney. Women in particular are moving more to the left this year than they expressed to Pew four years ago. White women under the age of 50, for example, are 19 points more supportive of the Democrat than they were then. White women 50 and over are 15 points more supportive.

The groups moving away from the Democratic candidate? White men — older white men, less educated white men. That's good news for Trump: If he's to have a shot in November, getting the backing of one of the largest segment of American voters isn't a bad way to do it. What's more, he does better in the Midwest than did Romney in 2012, reinforcing Trump's argument that he might be able to win states like Pennsylvania, which no Republican has won in six election cycles.

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At the very bottom, the group that's moved the most to the Republicans' advantage is black voters. Mind you, black voters still overwhelmingly back Clinton. It's just that they don't back her as strongly as they did Obama four years ago.