Trump made the comment in reference to Sen. Bernie Sanders, who Trump said made a bad choice by throwing his support behind Clinton.
"He made a deal with the devil," Trump said of Sanders. "She's the devil."
Trump's "devil" comment was just one in a series of bizarre comments and behaviors the bombastic billionaire exhibited Monday during a campaign swing through Ohio and Pennsylvania.
He sought to explain away the foreign policy blunder he made Sunday during an interview on ABC's This Week, in which he defended Russian President Vladimir Putin, seemingly without knowing the aggressive tactics Putin has taken in Eastern Europe to annex Crimea.
He went on to attack a fire marshal, who for safety reasons capped the number of people allowed into Trump's Columbus, Ohio, rally at 1,000.
And he later tweeted a photo of himself eating Kentucky Fried Chicken on his private jet.
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The Khans have not let up on their criticisms of Trump, who they say will cause a constitutional crisis in the United States with his policy to ban Muslims from traveling to the U.S. and who they accuse of having "a black soul."
His fight with the Khans has earned him the scorn of fellow Republicans, a number of whom have repudiated Trump's attacks on the Khan family — though they did not revoke their endorsements.
Even before the feud reached its peak, Trump's polling numbers took a plunge. He now trails Clinton by an average of 4.4% after the Democratic National Convention wrapped, according to RealClearPolitics.