Bernie Sanders and Hillary Clinton at Saturday’s debate. Donald Trump was attacked by name nine times during the debate, including five times by Clinton. (Jewel Samad/Agence France-Presse via Getty Images)

The day after the Democrats met here for their third presidential debate, much of the attention shifted to a candidate who wasn’t on the stage: the boisterous Republican front-runner, Donald Trump.

Trump — who was attacked by name nine times during Saturday night’s event, including five times by Hillary Clinton — returned fire during a pair of combative Sunday morning talk-show interviews. Focusing on Clinton, Trump called her weak and accused her of being a liar for making an unsubstantiated claim that Islamic State terrorists were using Trump’s comments on Muslims in its recruitment propaganda.

“It’s just another Hillary lie,” Trump said on NBC News’s “Meet the Press.” “She lies like crazy about everything, whether it’s trips where she was being gunned down in a helicopter or an airplane. She’s a liar and everybody knows that.”

The back-and-forth once again underscored Trump’s improbable and persistent dominance in the presidential race, whether during his months-long lead at the top of the Republican field or the extent to which Democrats have begun focusing on him as a possible GOP nominee. The barrage also illustrates the quickening pace of the nomination contests, with just six weeks to go before the Iowa caucuses on Feb. 1 followed by the New Hampshire primary eight days later.

“I think, and I say this straightforwardly, I think you have a pathological liar there,” said Democratic presidential candidate and Sen. Bernie Sanders (Vt.) on ABC’s “This Week,” referring to Trump’s debunked claim that thousands of Muslims in New Jersey were shown on television cheering after 9/11. “I think much of what he says are lies or gross distortion of reality.”

Especially since their own debate on Tuesday, Republican presidential candidates are also becoming increasingly vocal about their concerns with Trump’s rhetoric — specifically his suggestion that the United States should close its borders to most Muslims.

“Donald Trump had fallen out of the headlines, rightfully, because we had the largest terrorist attack in American history since 9/11,” Sen. Marco Rubio (Fla.) said Sunday on CBS’s “Face the Nation,” referring to the killing of 14 people in San Bernardino, Calif. “He wanted to get back in the headlines. And he came up with something spectacular and outrageous so that people would respond to it and he could recapture the headlines.”

Sen. Rand Paul (Ky.) called Trump’s front-runner status “deeply disturbing” on “Face the Nation.” “I think he will get wiped in a general election,” he said.

For Democrats, the billionaire serves as both a convenient foil and a strategic opportunity for the candidates to link his controversial comments to the remainder of the large GOP field.

During Saturday’s debate, former Maryland governor Martin O’Malley referred to Trump’s comments on national security and Muslims as the “fascist pleas of billionaires with big mouths.” Clinton warned that Trump’s rhetoric “fans the flames of radicalization.”

And Sanders used Trump’s comments on the economy to appeal to voters in the middle who might be attracted to his outspoken style.

“So what I say to those people who go to Donald Trump’s rallies, understand: He thinks a low minimum wage in America is a good idea,” Sanders said.

Clinton was dinged by fact-checkers for claiming during the debate that the Islamic State terrorist group was using Trump in recruitment videos. No such propaganda has surfaced, though terrorism experts have said that Trump’s comments on Muslims are being highlighted in extremist social media.

On “Meet the Press,” host Chuck Todd pressed Trump on his rhetoric and its possible benefit to terrorists, asking, “If you knew your words were being used, would you change your language?” Trump dismissed the question.

The real estate mogul also reiterated his praise of Russian President Vladi­mir Putin and defended Putin against accusations that he has assassinated political adversaries and journalists. Since 1992, 56 Russian and foreign journalists have been killed in the country, according to the Committee to Protect Journalists.

“Nobody has proven that he’s killed anyone. . . . He’s always denied it. It’s never been proven that he’s killed anybody,” Trump said on “This Week.” “You’re supposed to be innocent until proven guilty, at least in our country. It has not been proven that he’s killed reporters.”

The unusual embrace came after the Russian leader called Trump “talented without doubt” and “brilliant.” Trump has cited Putin’s praise as proof that a Trump administration would be able to work well with the Russians.

“What am I going to say — he’s a weak leader?” Trump said on ABC. “He’s making mincemeat out of our president. He is a strong leader.”

Former Florida governor Jeb Bush — who earlier in the weekend called Trump a “jerk” — said on “Face the Nation” that Trump was “not a serious man” and should not be praising Putin.

“We need a president that actually will stand up for American interests, whether it’s in Europe or in the Middle East,” Bush said. “And that’s how you create a better relationship with Putin. You don’t brag about how great a guy he is. He’s not. He kills journalists. Anybody that opposes him ultimately is pushed away.”

Meanwhile, tensions remained high between Sanders and the Democratic National Committee, which briefly blocked his access to voter data after the Sanders campaign inappropriately gained access to proprietary voter information gathered by Clinton.

During the debate, Sanders apologized to Clinton, and both candidates said they were eager to move on to other issues. But remarks by Sanders and his aides after the event suggest that raw feelings remain.

Appearing on CNN’s “Reliable Sources” on Sunday, Sanders campaign manager Jeff Weaver accused the DNC of leaking information about the controversy to the media to score “political points,” an accusation the DNC denied.

In addition, Sanders said in a television interview after the debate that the DNC deliberately scheduled two of the three debates so far on Saturday nights, when viewership would be low, in an effort to “protect” Clinton.

“I think everybody understands that Hillary Clinton, who I have a lot of respect for, is the establishment candidate,” Sanders said on WMUR, an ABC affiliate in New Hampshire. “Virtually the entire establishment is supporting her, including the leadership of the DNC.”

The DNC has defended the schedule of debates in which cable-channel events are typically held during the week and network-channel events are held on the weekend. The Democratic debates — two of which have been broadcast on the networks — have drawn less than half as many viewers as the Republican events. Early ratings data suggested Saturday’s ABC debate would be in line with last month’s Democratic debate on CBS, which averaged 8.5 million viewers.

Jennifer Palmieri, the Clinton campaign’s communications director, said that the campaign — believing that Clinton has excelled on the debate stage — would welcome a time slot geared toward a larger television audience.

“ABC and CBS are the ones that decided to put the debates on a Saturday night,” Palmieri said, naming the networks that broadcast the previous two debates. “Obviously, she does really great on these debates.”

Jose A. DelReal in Washington contributed to this report.