Businessman Donald Trump lived up to his sharp-edged reputation during the first Republican debate of the 2016 presidential campaign, sparring with moderators and other candidates Thursday night as everyone else on the 10-person stage struggled to stand out.

Trump became the center of the debate’s attention from the very beginning, when he was the only candidate who refused to forswear the idea of running a third-party campaign against the Republican Party, if he could not be its nominee.

“I cannot say, ‘I have to respect the person, who is not me,'” Trump said, as the crowd booed him. “We want to win, and we will win. But I want to win as the Republican. I want to run as the Republican nominee.”

Immediately, Kentucky Sen. Rand Paul attacked, saying that Trump is “hedging his bets,” and accusing him of being too close to the Clinton family. “He’s already hedging his bets on the Clintons,” Paul said, pointing in Trump’s direction. “He’s already hedging his bets, because he’s used to buying politicians.”

As the debate proceeded, it seemed to veer between two broad topics: America, and Donald Trump.

At times, the other nine candidates on stage debated serious policies – immigration, the nuclear deal with Iran, government surveillance, the future of Social Security. And then, at times, the debate veered to Trump himself: a sharp-edged candidate who can say things that would torpedo anybody else on stage.

Earlier in the debate, Trump defended himself against questions about his companies’ multiple bankruptcy filings, saying that he had “taken advantage” of the country’s bankruptcy to help his businesses.

“Out of hundreds of deals – hundreds – on four occasions, I’ve taken advantage of the laws of this country, like other people,” Trump said, in response to a question from moderator Chris Wallace. “The difference is, when somebody else uses those laws, nobody writes about it. When I use it, it’s like, ‘Oh, Trump, Trump, Trump.'”

In one of the non-Trump-related exchanges, New Jersey Gov. Chris Christie and Paul got into a heated argument about the limits of government surveillance, in an exchange that showcased two competing poles of Republican thought about security and privacy.

“I want to collect more records from terrorists, but less records from innocent Americans,” said Paul, the son of libertarian icon Ron Paul and one of the party’s strongest advocates for limiting government collection of Americans’ phone records and other data.

“That’s a completely ridiculous answer,” said Christie, a former federal prosecutor, who has said that the Sept. 11, 2001, terrorist attacks illustrated the need for broad-ranging collection of intelligence. “How are you supposed to know?”

“Use the Fourth Amendment! Get a warrant!” Paul responded.

Christie countered with the age-old insult that governors use against senators: “When you’re sitting in a subcommittee, blowing hot air about this,” the problem might seem easy, he said.

Paul retorted with the age-old insult that other Republicans use against Christie. “I don’t trust President Obama,” with records, he said. “I know you gave him a big hug.”

On a stage with 10 candidates, some seemed almost to disappear – neurosurgeon Ben Carson, Wisconsin Gov. Scott Walker, and Texas Sen. Ted Cruz all struggled for air time. Others broke with the hard-edged cultural conservatism that dominated the 2012 Republican primary. Ohio Gov. John Kasich said he had attended a same-sex wedding, and described that the Supreme Court decision legalizing same-sex marriage should be accepted as the law of the land.

Former Florida Gov. Jeb Bush defended an earlier statement calling immigration – including illegal immigration – “an act of love.”

“I believe that the great majority of people coming here illegally have no other option, and they want to provide for our family. But we need to control our border,” Bush said, pivoting to his plans to crack down on illegal immigration. He also returned to an idea that other Republicans have rejected: “There should be a path to earned legal status,” for illegal immigrants already in this country, Bush said. Others have rejected any pathway to legal status as “amnesty.”

But, time and again, the debate returned to Trump – and his long history of over-the-top statements, and flirtations with Democrats and Democratic ideas. At one point, Trump reiterated what – for any other candidate – would be a radioactive statement. He liked nationalized-single-payer health-care system, at least as it works in other countries.

“It works in Canada. It works incredibly well in Scotland. It could have worked” in the U.S. at one point, Trump said. Still, he said, he now supports a more modest set of health-care reforms, including allowing consumers to buy insurance across state lines.

Paul spoke up, saying that Trump was on the wrong side of everybody by praising a single-payer system. Trump brushed him off. “I don’t think you heard me. You’re having a hard time tonight,” he said.

In the debate’s second hour, there was a civil exchange between Christie and former Arkansas governor Mike Huckabee about how to reform Social Security. Christie urged some reforms: raising the age at which seniors are eligible for the benefits, and allowing well-off seniors to collect less. Huckabee resisted those changes, saying that any reduction in anyone’s Social Security benefits is “fundamentally lying to the people, and stealing from them.”

“He’s complaining about the lying and stealing – the lying and stealing has already occurred,” Christie said, meaning that the Social Security trust fund was already under-funded.

Earlier in the debate, Trump took credit for bringing the subject of immigration into the 2016 presidential campaign.

“If it weren’t for me, you wouldn’t even be talking about illegal immigration, Chris. You wouldn’t be talking. This wasn’t a subject,” Trump said to one moderator, Fox News’ Wallace.

Wallace also tried to press Trump to produce evidence for a key Trump claim: that the Mexican government is actively dispatching illegal immigrants over the border. Trump cited only conversations with “Border patrol. People, that I deal with, that I talk to, they say, this is what’s happening.”

He said he remained convinced that the Mexican government was orchestrating immigration, in order to avoid paying benefits and other costs associated with its own citizens. “The stupid leaders of the United States will do it for ’em, and that’s happening, whether you like it or not.”

At the beginning of the debate, Paul had shown himself willing to attack Trump. But not everyone thought that was wise.

“They say we’re outspoken, we need to take lessons from Donald Trump,” Ohio Gov. John Kasich said, when Wallace asked him to critique Trump’s assertion. “He’s hitting a nerve.”

Florida Sen. Marco Rubio, also prompted to criticize Trump, also refused.

“People are frustrated,” he said.

Just as in 2012, the primary showcased the GOP’s combative side. The crowd cheered when a moderator mentioned that Cruz had called Senate Majority Leader Mitch McConnell of Kentucky, one of the top Republicans in Washington, a “liar.” And onstage, Trump continued to be the best at embodying that edge. When moderator Megyn Kelly asked Trump about past statements criticizing women for their appearance, Trump responded by saying, “Only Rosie O’Donnell.”

He then turned on Kelly herself, suggesting she was on thin ice by even asking the question.

“I don’t frankly have time for total political correctness. And to be honest with you, this country doesn’t have time, either,” Trump said, as the crowd cheered. “If you don’t like it, Megyn, I’m sorry. I’ve been very nice to you, although I could maybe not be, based on the way you have treated me.”

Other candidates sought to distinguish themselves in the debate’s first few minutes. Huckabee attacked Planned Parenthood by saying that it sold parts of aborts fetuses “like parts to a Buick.” Rubio, whose parents were Cuban immigrants, said that he could debate Hillary Rodham Clinton about what’s best for families living paycheck-to-paycheck, because he had lived that way.

Bush, the son and brother of presidents, responded to a question about his family legacy by saying that “They called me Veto Corleone,” in Florida, he said, because he had vetoed so many bills. “I’m my own man.”

The two-hour debate, held at the QuickenLoans Arena in Cleveland and televised on Fox News Channel, ties the record for most candidates in any primary-season debate. And that’s not even the whole field: earlier Thursday evening, seven other, lower-polling candidates held a separate debate in the same arena.