Susan Page

USA TODAY

Donald Trump is ending his presidential bid the same way he began it: defiant and provocative, breaking campaign norms and ignoring experts’ advice — and becoming the nation’s first presidential nominee in memory to say he wouldn’t necessarily accept the election returns on Nov. 8.

At the third and final debate in Las Vegas on Wednesday, Trump ticked off a list of grievances: Voter fraud he claims could let millions of ineligible people cast ballots. Charges of sexual misconduct against him that he said were “probably” generated by opponent Hillary Clinton’s campaign. A news media he labeled as corrupt. And the stunning suggestion that he just might not concede the election if he lost.

“I will look at it at the time,” the Republican nominee told moderator Chris Wallace of Fox News. “I’ll keep you in suspense.”

Clinton called that response “horrifying.”

Will Trump accept election results? He'll get back to you

Vegas showdown: Catch up on what you missed in the final debate

With charge and countercharge — each accusing the other of being “unfit” for the White House — it was the most brutal presidential debate of the television age. The candidates did not shake hands before the debate began or when it ended.

Voters looking for an uplifting conclusion to an unrelentingly negative campaign didn’t get it here.

At this point, winning the White House would require the billionaire businessman and reality TV star to stage the most dramatic political comeback in modern American history. Clinton’s national lead is the largest any candidate has held in decades three weeks before Election Day. But his fierce new message — that journalists and the political establishment are working in collusion against him to rig the election — helps guarantee that his campaign will have a continuing impact even if Clinton prevails.

In some ways, Trump is like a bull trying to make sure as many teacups as possible are shattered before he leaves the china shop.

Indeed, he didn’t seem to be making much of an effort during the debate to reach out to independents and other swing voters by adopting a more presidential mien, or to reassure skeptical voters that he had the temperament for the job he seeks. “Such a nasty woman,” he muttered while Clinton was speaking. Citing investigations into her use of a private email server when she was secretary of State, he called her a “liar” who “shouldn’t be allowed” to run for president.

He flatly denied allegations of aggressive sexual misconduct from about a dozen women who have come forward since the second debate. “It was lies and it was fiction,” he said. “I think they want either fame or her campaign did it,” pointing at Clinton.

“Every time Donald doesn’t think things are going in his direction, he claims everything is rigged against him,” Clinton said. She said she was “appalled” by his unwillingness to promise to accept the election results: “He is denigrating; he’s talking down our democracy.”

Trump to Clinton: 'Such a nasty woman'

Trump blames Clinton campaign for sexual misconduct allegations

Of course, Clinton had her own difficulties. She was on the defensive over the WikiLeaks release of thousands of emails to and from John Podesta, now her campaign chairman, that among other things contain purported excerpts from cozy speeches she delivered to big bankers. She denied allegations that there had been conflicts in interest in fundraising by the Clinton Foundation while she was secretary of State.

Trump dubbed that a “criminal enterprise.”

His burn-down-the-house strategy is designed to excite his core supporters and discourage Clinton’s supporters from showing up to vote. It also is likely to have an impact after the election on a President Hillary Clinton, if she wins, and on a divided Republican Party. The discontent he has tapped more effectively than any other political figure this year, winning him the GOP nomination against the odds, isn’t going away after the ballots are counted.

Trump’s allegations of a fixed election, while not backed by evidence, could raise questions among some about the legitimacy of Clinton’s victory, just as his discredited suggestions that Barack Obama wasn’t born in the United States raised questions. His accusations of criminal misconduct by Clinton, which prompts chants of “Lock Her Up!” at his rallies, could encourage congressional Republicans to demand investigations of the new president. His hard line on immigration and trade could make it more difficult for GOP lawmakers to consider compromises that would help get legislation passed.

He has changed the political landscape itself — blurring the lines between politics and celebrity, and crossing the traditional boundaries about what is appropriate to say and do in a political campaign.

“Trump has created a roiling force that will make national politics and policymaking an even bumpier ride than it has been in recent years,” predicts Steven Schier, a political scientist at Carleton College in Northfield, Minn., and co-author of Polarized: The Rise of Ideology in U.S. Politics. He calls it “a new populist movement that will vex the GOP and challenge Hillary Clinton throughout her first term, should she be elected.”