He said that Vermont Sen. Bernie Sanders should have stayed in the race and not thrown his support behind Clinton.
"He would've been a hero," Trump said. "But he made a deal with the devil. She's the devil. He made a deal with the devil."
Trump has linked Clinton to Satan before, saying Sanders "sold his soul to the devil," but this is the first time Trump has been so explicit. Such language adds to the barrage of other insults he levels at her regularly, the most popular among his supporters being the moniker "crooked Hillary."
He added that he was eager to meet Clinton this fall on the debate stage, saying, "I look so forward to the debate with Hillary. I look so forward."
Meanwhile, Trump adviser Ed Brookover has been fired by the campaign, sources said. Brookover, Ben Carson's former campaign manager, most recently served as a liaison between the campaign and the Republican National Committee.
It was not immediately clear why Brookover was fired. He could not immediately be reached for comment.
Additional reporting by Katherine Faulders.