Donald Trump said Monday on the campaign trail he worries the general election in November will be "rigged," and later called rival Hillary Clinton "the devil."

"I'm afraid the election is going to be rigged, I have to be honest," the Republican nominee for president said at a rally in Ohio.

Trump's remarks did not mention the controversy generated by his criticism of the parents of a slain Muslim U.S. soldier. He didn't elaborate on the comment.

Trump said he felt the Democrats had fixed their primary system so Clinton could defeat Bernie Sanders and claimed the Republican nomination would have also been stolen from him had he not won "by such tremendous margins."

If the remark was more than just an offhand comment, it would seem to threaten the tradition of peacefully contested elections and challenge the very essence of a fair democratic process. He repeated the charge Monday night on Fox News Channel's "Hannity," asserting that the election "is going to be rigged" and that Republicans should watch closely.

Associated Press requests to Trump's campaign for additional explanation were not returned.

Speaking in Pennsylvania later on Monday, Trump said Sanders had "made a deal with the devil" in supporting Clinton.

"She's the devil," Trump said.

Trump's Ohio rally was held after President Barack Obama spoke at the annual convention of the Disabled American Veterans in Atlanta, implicitly admonishing Trump by saying no one has given more for American freedom and security than the families of those who have died for their country. Obama's statement was the latest rebuke from a politician, following comments critical of Trump from both parties over the weekend.

Trump had taken issue with the Muslim parents of Army Capt. Humayun Khan, who was killed in Iraq over a decade ago. They spoke out against Trump at the Democratic National Convention, sparking a back-and-forth between Trump and the parents in the press.

Trump spoke to reporters before the Ohio rally, but did not address the Khan family controversy, NBC News' Hallie Jackson reported. He also made no mention of the issue in Pennsylvania, though he said there that if he doesn't win on Nov. 8, he will consider running for president "a tremendous waste of time, energy and money."

"I would have rather lost a year ago, it would have been easier," he told the crowd in a Harrisburg-area high school, urging them to bring their friends to vote.

Trump said "it takes guts" to run for president and he could "have a very nice life right now."

"I don't have to be with you people, ranting and raving," Trump said.

While Trump may suspect some wrongdoing in the election, he sounded a more optimistic note about his own campaign at the Ohio rally, saying over 500,000 small donors had contributed $35.8 million in the last month, with an average donation of $69.

If true — he said that his campaign would be announcing the figures soon — it would nearly equal the $39.4 million he received in total contributions he received from April 2, 2015 to June 30, 2016, according to FEC filings.

Trump compared himself to Sanders, who funded his presidential bid through small donors. Trump said the money both of them have collected is evidence of "a movement."

Trump and Clinton both must report their July fundraising information to federal regulators by Aug. 20.

The Associated Press contributed to this report.