In a remarkable statement that seemed to cast doubt on American democracy, Donald J. Trump said Wednesday that he might not accept the results of next month’s election if he felt it was rigged against him — a stand that Hillary Clinton blasted as “horrifying” at their final and caustic debate on Wednesday.
Mr. Trump, under enormous pressure to halt Mrs. Clinton’s steady rise in opinion polls, came across as repeatedly frustrated as he tried to rally conservative voters with hard-line stands on illegal immigration and abortion rights. But he kept finding himself drawn onto perilous political territory by Mrs. Clinton and the debate’s moderator, Chris Wallace.
He sputtered when Mrs. Clinton charged that he would be “a puppet” of President Vladimir V. Putin of Russia if elected. He lashed out repeatedly, saying that “she’s been proven to be a liar on so many different ways” and that “she’s guilty of a very, very serious crime” over her State Department email practices. And by the end of the debate, when Mrs. Clinton needled him over Social Security, Mr. Trump snapped and said, “Such a nasty woman.”
Mrs. Clinton was repeatedly forced to defend her long service in government, which Mr. Trump charged had yielded no real accomplishments. But she was rarely rattled, and made a determined effort to rise above Mr. Trump’s taunts while making overtures to undecided voters.
She particularly sought to appeal to Republicans and independents who have doubts about Mr. Trump, arguing that she was not an opponent of the Second Amendment as he claimed, and promising to be tougher and shrewder on national security than Mr. Trump.
But it was Mr. Trump’s remark about the election results that stood out, even in a race that has been full of astonishing moments.
Every losing presidential candidate in modern times has accepted the will of the voters, even in extraordinarily close races, such as when John F. Kennedy narrowly defeated Richard M. Nixon in 1960 and George W. Bush beat Al Gore in Florida to win the presidency in 2000.
Mr. Trump insisted, without offering evidence, that the general election has been rigged against him, and he twice refused to say that he would accept its result.
“I will look at it at the time,” Mr. Trump said. “I will keep you in suspense.”
“That’s horrifying,” Mrs. Clinton replied. “Let’s be clear about what he is saying and what that means. He is denigrating — he is talking down our democracy. And I am appalled that someone who is the nominee of one of our two major parties would take that position.”
Mrs. Clinton then ticked off the number of times he had deemed a system rigged when he suffered a setback, noting he had even called the Emmy Awards fixed when his show, “The Apprentice,’’ was passed over.
“It’s funny, but it’s also really troubling,” she said. “That is not the way our democracy works.”
Mrs. Clinton also accused Mr. Trump of extreme coziness with Mr. Putin, criticizing him for failing to condemn Russian espionage against her campaign’s internal email.
When Mr. Trump responded that Mr. Putin had “no respect” for Mrs. Clinton, she shot back, in one of the toughest lines of the night: “That’s because he’d rather have a puppet as president of the United States.”
“No puppet, no puppet,” Mr. Trump sputtered. “You’re the puppet.” He quickly recovered and said, “She has been outsmarted and outplayed worse than anybody I’ve ever seen in any government, whatsoever.”
With 20 days left before Election Day and early voting already underway in Florida, Ohio and several other key states, the debate felt less like an argument between equals than a last-ditch attempt by a fading candidate, Mr. Trump, to save himself.
Mr. Trump sought throughout the debate to recover from a politically damaging three weeks. He has been unable to gain traction in the polls from his strategy of assailing the Clintons as corrupt and immoral; the news media as biased and bent on rigging the election against him; and the nine women who have come forward to accuse him of unwanted sexual advances as liars and, in some cases, unattractive.
Mr. Trump said, in response to a question from the debate moderator, Chris Wallace of Fox News, that the claims of the women had been “debunked” and that they had been put forward by Mrs. Clinton’s campaign.
But after he denied ridiculing the looks of the women accusing him of sexual harassment — “I did not say that,” he repeated three times — Mrs. Clinton repeated nearly verbatim his two comments from last week about the appearances of a pair of his accusers.
“Donald thinks belittling women makes him bigger,” she said. “He goes after their dignity, their self-worth; and I don’t think there is a woman anywhere who doesn’t know what that feels like.”
After Mrs. Clinton finished an extended condemnation, Mr. Trump said only: “Nobody has more respect for women than I do, nobody.”
In contrast to their two previous debates, the 90-minute discussion covered significant substantive ground. On immigration, Mr. Trump argued that Mrs. Clinton wanted to give illegal immigrants “amnesty” and that “she wants to have open borders.”
“We have to have strong borders, we have to keep the drugs out of our country — right now we’re getting the drugs, they’re getting the cash,” he added. “We have some bad hombres here, and we’re going to get them out.”
Mrs. Clinton recalled meeting a young girl in Las Vegas whose parents had been threatened, and noted that Mr. Trump has said that every illegal immigrant would ultimately be subject to deportation.
“I don’t want to rip families apart,” Mrs. Clinton said. “I don’t want to see the deportation force that Donald has talked about in action in our country.”
At several points, Mrs. Clinton tried to bait Mr. Trump into an outburst, such as when she said that he “choked” during his meeting this summer with the president of Mexico when he did not press him on Mexico paying to build a border wall.
But Mr. Trump pivoted to attack former President Bill Clinton’s administration for supporting the North American Free Trade Agreement and assailed Mrs. Clinton for her past comments supporting “open borders” in the Western Hemisphere.
Mr. Trump also called the Clinton Foundation “a criminal enterprise.” Mrs. Clinton returned fire by ridiculing Mr. Trump’s foundation, which she noted purchased “a six-foot portrait of Donald.”
“I mean, who does that?” she asked.
The two candidates also tangled over abortion rights. After initially declining to flatly say whether he would support overturning Roe v. Wade, the 1973 Supreme Court decision that legalized abortion, Mr. Trump conceded that the justices he would appoint to the court would do just that.
“If we put another two or perhaps three justices on, that’s really what will happen,” he said. “That’ll happen automatically in my opinion.”
Mrs. Clinton responded with a full-throated defense of Roe and abortion rights.
“The government has no business in the decisions that women make,” she said.
Mr. Trump retorted, “If you go with what Hillary is saying, in the ninth month you can take the baby and rip the baby out of the womb of the mother just prior to the birth of the baby.”
Mrs. Clinton appeared visibly angry. “You should meet with some of the women I’ve met with,” she said, accusing him of using “scare rhetoric.”
Mrs. Clinton used the opening question about the Supreme Court to make a broad appeal to voters to consider the future of the United States under her presidency or a Trump administration. “What kind of country are we going to be? What kind of opportunities are we going to provide for our citizens, what kind of rights will Americans have?”
Mr. Trump asserted that if Mrs. Clinton won, the Second Amendment would become “a very, very small replica of what we have now.” He also said he would appoint justices who “will interpret the Constitution the way the founders want it interpreted.”
Mrs. Clinton quickly tried to undercut Mr. Trump on guns.
“I support the Second Amendment,” she said, noting that she had lived in Arkansas and represented upstate New York where many gun owners lived. “When I think about what I need to do, we have 33,000 people a year who die from guns. I think we need comprehensive background checks” and to close loopholes that make it easier for Americans to buy guns.
On the economy, Mrs. Clinton described Mr. Trump as a hypocrite, accusing him of crying “crocodile tears” over manufacturers moving abroad while noting that he uses foreign steel for his hotel in Las Vegas.
That prompted a ferocious counterattack from Mr. Trump, demanding why she had not done more to improve the economy during her years in public life.
“Why the hell didn’t you do it over the last 15 or 20 years,” he demanded, adding: “The one thing you have over me is experience, but it’s bad experience.”
Mrs. Clinton, clearly prepared for him to return to this line of attack, responded with a carefully prepared salvo.
She compared what the two of them had been doing since the 1970s, highlighting her public service accomplishments and ridiculing him for borrowing money from his father, mocking a beauty queen as “an eating machine” and hosting a reality television show.
“On the day when I was in the Situation Room, monitoring the raid that brought Osama bin Laden to justice, he was hosting “The Celebrity Apprentice,’” Mrs. Clinton said.
Mr. Trump defended himself by boasting about his business success and said the country would be well served if it was run in the fashion of his company.
Mrs. Clinton, reaching for not just a win but a mandate, made both direct and more subtle appeals to Republican voters. She noted that in the 1980s Mr. Trump had criticized Ronald Reagan over his stewardship, twice invoking the name of the late president revered by so many Republicans.
Remarkably, Mr. Trump demanded additional time to speak so he could note that he did, in fact, disagree with Reagan over trade. Mrs. Clinton, in that moment, came off as more respectful to Republican history.
“I would like to say to everyone watching tonight that I’m reaching out to all Americans, Democrats, Republicans and independents,” she said, “because we need everybody to help make our country what it should be.”