Donald Trump's key demographic, white men without a college degree, could swing the race for the Republican if they decide to vote in the upcoming election, says Karl Rove.

In 2012, President Barack Obama won re-election by just under 5 million votes, according to FiveThirtyEight, but 24 million white men with no higher education could have changed the tide, if they had voted. Today, Trump holds the support of the majority of men in that demographic, and getting them to the polls could be the key to beating Hillary Clinton.

"Exit polls from 2012 show that Mr. Romney won 59 percent of white voters, and that whites constituted 72 percent of the turnout," Rove wrote in an op-ed for The Wall Street Journal. "The Trumpers say their man can win by boosting those figures only slightly. Increase the GOP's share of the white vote a few points, say to 62 percent. Raise the white turnout to 74 percent or 75 percent. Voilà, President Trump."

Trump's support from uneducated white men can be traced to three main interests, according to House Minority Leader Nancy Pelosi, D-Calif., who said Wednesday, "I think that, so many times, white, non-college-educated white males have voted Republican. They voted against their own economic interests because of guns, because of gays, and because of God, the three G's, God being the woman's right to choose."

"In the GOP primaries, two Republicans based their campaigns on the 'missing five million,' but they differed on who the absent voters were," Rove continued. "Texas Sen. Ted Cruz contended that they were white evangelicals. Mr. Trump argued that they were white blue-collar workers. But the two agreed that the path forward was to adopt a populist anti-establishmentarianism."

Rove cites exit polls from the last four presidential elections, showing that white voter turnout decreased each time.

"The country is becoming more racially diverse," Rove adds. "It will be nearly impossible for Mr. Trump to keep the white share flat, let alone increase it."