Protesters hold up signs before a campaign rally for Republican presidential candidate Donald Trump at Lenoir-Rhyne University March 14, 2016 in Hickory, North Carolina. (Photo by Sean Rayford/Getty Images)

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ATLANTA, Ga. (CBSMiami/AP) — Wanda Melton has voted for every Republican presidential candidate since Ronald Reagan in 1980, but now the Georgia grandmother plans to cross over to support Democrat Hillary Clinton.

“I’m not a real fan of Hillary,” Melton says from her office in Atlanta. “But I think it would just be awful to have Donald Trump.” She adds: “I cannot in good conscience let that happen.”

Melton is among a particular group of voters, whites with college degrees, who are resistant to Trump. Their skepticism comes as an ominous warning as Trump struggles to rebuild even the losing coalition that Mitt Romney managed four years ago.

College-educated whites made up more than one-third of the electorate in 2012. Polls suggest Trump trails Clinton with those voters, especially women.

“Donald Trump simply cannot afford to lose ground in any segment of the electorate” that supported Romney, said Florida pollster Fernand Amandi. Romney’s strength with that group, for example, made for a close race in Florida, where President Barack Obama won by less than 75,000 votes out of more than 8.4 million cast.

Some Republicans worry Trump’s approach — his unvarnished, sometimes uncouth demeanor and his nationalist and populist arguments — guarantees his defeat, because the same outsider appeal that attracts many working class and even college-educated white men alienates other voters with a college degree.

Ann Robinson, 64, is a lifelong Republican in a Trump’s home state of New York, a Democratic stronghold that the real estate tycoon cites as an example of where he can “expand the map.” Robinson sneers at the proposition and says she’ll vote for Clinton.

“It’s just not a reasonable movement,” she says of Trump’s populist pitch. “I’m not sure he can actually be their savior. She has so much more experience. Trump has nothing.”

Mary Darling, 59, is an Illinois Republican who said she won’t vote for Trump or Clinton. “If they could just soften his edges, people would flock to him, but that’s just not going to happen,” she said.

Lew Oliver, chairman of the Orange County Republican Party in Florida, says he’s prepared for an uphill fight in no small part because of Trump’s struggle among more educated voters. “The fundamentals aren’t in our favor, and some of his comments aren’t helping,” Oliver said.

Romney drew support from 56 percent of white voters with college degrees, according to 2012 exit polls. Obama notched just 42 percent, but still cruised to a second term.

A Washington Post-ABC News poll taken in June found Clinton leading Trump among college-educated whites 50 percent to 42 percent.

Polling from the nonpartisan Pew Research Center pointed to particularly stark numbers among white women with at least a bachelor’s degree. At this point in 2008 and 2012, that group of voters was almost evenly divided between Obama and the Republican nominee. This June, Pew found Clinton with a 62-31 advantage. Conversely, Pew found Trump still leads, albeit by a slightly narrower margin than did Romney at this point, among white women with less than a bachelor’s degree.

Should Trump fail to even replicate Romney’s coalition, he has little hope of flipping many of the most contested states that Obama won twice, particularly Florida, Colorado and Virginia. Trump’s struggles among college whites have Democrats eyeing North Carolina, which Obama won in 2008 before it reverted back to Republicans, and even GOP-leaning Arizona and Georgia.

The education gap for Trump isn’t new.

Exit polls in the Republican primaries found him faring better among less educated groups. Trump particularly struggled with better educated Republicans when Florida Sen. Marco Rubio, R-Fla., was in the presidential race.

Republican pollster Greg Strimple of Idaho says the gap is understandable. Voters without a college education, he said, are more likely to be struggling financially, to feel alienated from the political class Trump rails against and to find solace in his promise to stop illegal immigration.

College educated voters “may have had relatively stagnant incomes, but they can still look at their 401(k)s and think about the future,” Strimple said. “They’re free to care more about things like tone.”

Clinton’s campaign sees the persuadable portion of the electorate as being made up largely of women, many with college degrees. It has tried to reach them by hammering Trump as “dangerous” and “temperamentally unfit” for the job, while her initial general election advertising blitz focuses on her achievements in public life.

Strimple said Trump must counter that with a constant “indictment of the last eight years, an indictment of Hillary Clinton. That can get some of those voters back.”

The question for Trump, though, is how many Wanda Meltons are already lost. “He’s just not in control of himself,” she says. “That personality type is not suited either to leadership or protecting the country.”

(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)