 -- President Obama took aim today at Donald Trump’s insistence that he may not accept the results of the presidential election, especially if he loses -- saying the comments were "not a joking matter."

“When you suggest rigging or fraud without a shred of evidence, when last night at the debate, Trump becomes the first major party nominee in American history to suggest that he will not concede despite losing the vote, and then says today that he will accept the results if he wins? That is not a joking matter,” Obama said during a rally on behalf of Hillary Clinton in Florida.

Obama’s remarks came after Trump doubled down on his refusal to say he’d accept the results of the election, saying at a rally in Ohio, “I will totally accept the results of this great and historic presidential election. If I win."

The night before, at Wednesday's debate, Trump said he would not predetermine whether he’d accept the outcome on Nov. 8.

“I'll tell you at the time. I'll keep you in suspense, okay?" he said.

Earlier Thursday, the president took to Twitter to congratulate Hillary Clinton on her performance in last night's third and final presidential debate of the 2016 election.

First lady Michelle Obama and Vice President Joe Biden also campaigned today in states the Democrats hope to win in the presidential election. Biden was in the swing state of New Hampshire, while the first lady was bound for the typically red state of Arizona, which Democrats hope is within striking distance for them this year.