For Trump, one challenge is a socioeconomic split in the white vote. He has strong support among white voters without college degrees, but has seen an erosion in the traditional support for Republican nominees among white voters with college degrees.

This has been a central dynamic of the campaign, and Clinton campaign officials view it as a potentially decisive factor in an electoral map that has shifted since the last election.

The split between college-educated and non-college-educated white voters has moved states such as Colorado and Virginia toward the Democrats, while giving Trump more hope of capturing industrial states in the Midwest such as Michigan, Pennsylvania and Ohio, where there is a higher concentration of non-college-educated voters.

Democrats remain skeptical that Trump, who boasts of his ability to bring new Republican voters to the polls, can crack what in recent cycles has been a “blue wall” in the upper Midwest.

“Trump is making a last bet on white, non-college-educated men in Pennsylvania, Michigan and Wisconsin,” Podhorzer said. “That’s been tried by Republican candidates before, and it hasn’t worked.”