CLEVELAND—The most striking argument from the podium during the Republican convention’s first nights was Donald Trump Jr.’s claim that his father had more respect for blue-collar “street smarts” than white-collar book smarts earned at “fancy colleges.”

It was yet another instance of cultural signaling from the Trump campaign toward the working-class white voters who have anchored his support from the outset. But it also underscored the distance between the unconventional GOP nominee and the college-educated whites who have long been central to the party’s coalition.

Those white-collar whites are the group in which Trump’s performance most conspicuously lags behind other recent Republican nominees. They are also the group that appears most conflicted about the choice between Trump and Hillary Clinton.

Both candidates have reason for anxiety about these voters’ potentially pivotal role. For Trump it means converting a group much cooler to him than blue-collar whites even through the Republican primaries. And for Clinton it means holding a constituency that no Democratic presidential nominee has carried in the history of modern polling dating back to 1952. “How long can she continue to outrun President Obama by double digits among college whites?” frets one top Democratic strategist working on an independent pro-Clinton effort.  “It does make you a little nervous.”

The Melania Trump plagiarism controversy was a reminder that unpredictability is Donald Trump’s only reliable companion. Yet some patterns in the race are already hardening.

In most national polls, Trump appears on track to match or exceed the 62 percent support among white voters without a college education that Mitt Romney, according to exit polls, captured in 2012. Some Trump advisers believe he could blow past that elevated level to reach the two-thirds that Reagan won in 1984; the key may be reinforcing his position among blue-collar white women, who appear considerably more ambivalent about him than their male counterparts.

Conversely, Trump seems at risk of losing even more ground among non-white voters, who already preferred Obama to Romney in 2012 by a resounding combined margin of 80-17 in the exit polls. Recent polls in Pennsylvania and Ohio found Trump drawing literally no support from African Americans. And although the samples of Latino voters in many media polls are too small to measure reliably, larger recent surveys released by the two major Spanish-language television networks (Telemundo and Univision) each showed Trump attracting fewer than one-in-five Hispanics, a significant drop even from Romney’s meager 27 percent.

That leaves college-educated whites as the campaign’s most closely contested—and conflicted—major constituency. National surveys released this week by CNN, NBC/Wall Street Journal and ABC/Washington Post all showed the same result, with Trump leading Clinton among those white-collar whites by a single percentage point. Polls consistently show Clinton leading with college-educated white women (who narrowly titled against Obama last time) and usually have Trump leading among college-educated white men, though not by as much as Republicans typically do.

This isn’t nearly enough for Trump. Even if he grows among blue-collar whites to Reagan ’84 levels, his struggles among non-whites means he likely can’t win without capturing either slightly below or just above 60 percent of college-educated whites, depending on how large a share of the vote they comprise. For comparison, the exit polls showed Romney winning 56 percent of white-collar whites last time.

So far, the swing-state advertising blitz from Priorities USA, the super PAC supporting Clinton, has focused principally on preventing Trump from getting anywhere near that level. With ads like “Grace”—the arresting spot in which two white professional-looking suburban parents of a daughter with spina bifida express outrage at Trump mocking a disabled reporter—the PAC is “going for college whites right now,” said the veteran Democratic strategist. “The ceiling [on his overall support] is put in place by limiting his growth among college whites.”

Trump is indeed facing mountainous skepticism among those well-educated whites. In the ABC/Post poll, 60 percent of them said he’s not qualified to be president. (Nearly as many said Clinton was qualified.) Half of college-educated whites in that survey said they believed Trump was biased against minorities and women. In other surveys, white-collar whites strongly prefer Clinton for handling foreign policy, race relations, and domestic social issues like abortion.

Polls have also shown college-educated whites are much more positive than their blue-collar counterparts toward trade, immigration, and America’s growing racial diversity—all of which makes them a difficult audience for Trump’s insular agenda of defensive nationalism. With “all of these big exciting changes in society … there are people who have benefited and people who haven’t,” says the Republican pollster Kristen Soltis Anderson. “And if you have a college degree, you are more likely to [believe] those changes … have benefited you.”

But these college-educated whites also express huge doubts about Clinton’s honesty and capacity to change Washington. And in the ABC/Post poll, they narrowly prefer Trump for handling the economy. Overall, 66 percent of college-educated whites in the survey expressed an unfavorable view toward Clinton, virtually identical to the 68 percent who viewed Trump negatively.

The large number of college-educated whites, especially women, that view Trump as unqualified, temperamentally unsuited to the presidency, and racially divisive represent arguably the single largest obstacle between him and the White House. But it’s a sobering thought for Democrats that their final line of defense against the blustery billionaire is composed of voters who also don’t think very much of Hillary Clinton.