Harry Enten, writing for of Fivethirtyeight.com:

Donald Trump’s strategy in this campaign has been fairly clear from the beginning: Drive up Republican support among white voters in order to compensate for the GOP’s shrinking share among the growing nonwhite portion of the electorate. And Trump has succeeded in overperforming among a certain slice of white voters, those without a college degree. But overall, the strategy isn’t working. Trump has a smaller lead among white voters than Mitt Romney did in 2012, and Trump’s margin seems to be falling from where it was when the general election began.

And:

To be more specific, Trump is trading one type of white voter for another. Even as he piles up support among white men without a college degree, he’s on track for a record poor performance for a Republican among white voters with a degree. And right now, that tradeoff is a net negative for Trump, compared with Romney. If a ton of new white voters without a degree flooded into the electorate, that could change the math for Trump. But such a surge doesn’t look like it’s in the offing.