During the final presidential debate with Clinton on Wednesday night, the Republican candidate refused to say whether he would follow years of tradition and concede if he doesn’t win the White House on Nov. 8. He has laid the groundwork by complaining for weeks that the system is ‘‘rigged’’ against him and in favor of Clinton.

‘‘That is not a joking matter,’’ Obama said at a campaign rally for Trump’s rival, Democrat Hillary Clinton.

MIAMI GARDENS, Fla. — Calling it ‘‘dangerous,’’ President Barack Obama said Thursday that Donald Trump’s attempt to ‘‘sow the seeds of doubt’’ about the integrity of elections in America undermines U.S. democracy and does the work of the nation’s adversaries.


‘‘I will tell you at the time. I’ll keep you in suspense,’’ Trump said. Clinton responded by calling the statement ‘‘horrifying.’’

On Thursday, Trump tried to make light of the situation while campaigning in Ohio.

‘‘I would like to promise and pledge to all of my voters and supporters and to all of the people of the United States that I will totally accept the results of this great and historic presidential election,’’ he said. After pausing for several seconds, he added: ‘‘If I win.’’

Obama, who has felt the sting of losing an election and has conceded defeat, wasn’t buying it. He said Trump’s comments were further evidence of his lack of fitness for the office.

‘‘All the Republicans — not all, but most — have acknowledged there’s no way to rig an election in a country this big,’’ Obama said. ‘‘He doesn’t even worry if what he says is true. It’s just about him worried that he’s losing, which means he really doesn’t have what it takes to hold this job.’’

He urged Floridians to take advantage of the opportunity to vote early, beginning on Monday.


‘‘There’s only one way we lose this election. Just one. If we don’t turn out to vote,’’ Obama said. ‘‘Only way. We got to do it big. We got to leave no doubt.’’

Obama said Trump is the first major party nominee in U.S. history to suggest he will not accept a loss.

‘‘That is dangerous,’’ Obama said. ‘‘Because when you try to sow the seeds of doubt in people’s minds about the legitimacy of our elections, that undermines our democracy. ... You’re doing the work of our adversaries for them because our democracy depends on people knowing that their vote matters.’’

Earlier in the week, Obama suggested that Trump ‘‘stop whining’’ and get to work trying to win people’s votes.