The GOP presidential frontrunner pledged to protect Social Security, touted his opposition to free trade, and continued to defend government use of eminent domain to take property for private development.

But Trump’s denunciation of George W. Bush’s invasion of Iraq may have been his riskiest departure from the party line.

The 43rd president has regained popularity with conservative voters. And while the view that the Iraq invasion was a disaster is shared among Democrats, Republican primary voters in ardently pro-military South Carolina and other southern states are a different story.

“They lied,” Trump said, taking aim at the former president, just ahead of George W. Bush’s visit to South Carolina to stump for his brother Jeb.

“They said there were weapons of mass destruction,” Trump said, his voice raised. “There were none and they knew there were none.”

Jeb Bush countered with a barb. “While Donald Trump was building a reality TV show, my brother was building a security apparatus to keep us safe,” the former Florida Governor said.

Trump responded by interrupting. “The World Trade Center came down on his watch,” he yelled, in one of several instances in which he drew boos from the crowd, which he claimed was packed with his rivals’ donors.

Trump holds a commanding 18.5 percentage point lead in Real Clear Politics’ average for the South Carolina GOP primary. With a week until voting begins in the state, he will be hard to catch. But his boorish and thin-skinned performance on Saturday, which included frequent interruptions of his rivals, could slow his momentum.

Trump’s battles with Bush set a tone for a debate colored by pointed and, at times, schoolyard-level insults. At a debate held just a few hours after news of the sudden death of conservative Supreme Court Justice Antonin Scalia, the GOP candidates honored the late jurist’s pugilistic argumentative style but not his erudition.

Bush, who stumbled over his words early but grew crisper as the event progressed, hit Trump every chance he had. Responding to Trump’s description of Bush as “weak on immigration,” Bush told Trump it is “weak to denigrate” women, Hispanics, and disabled people. Trump has mocked members of each group.

Trump took aim at Sen. Ted Cruz, who polls second in South Carolina. “You are the single biggest liar,” he told Cruz, after the Texas senator claimed Trump would nominate liberals to the Supreme Court.

“He’s a nasty guy,” Trump added.

Cruz told Trump: “Adults learn not to interrupt each other.”

Cruz also had his hands full with Sen. Marco Rubio of Florida, who worked to rebound from his disastrous performance at the previous Republican debate in New Hampshire.

Cruz claimed that Rubio supported “amnesty” for illegal immigrants by offering a comprehensive immigration reform bill with Democrats. Cruz also said Rubio had pledged on Univision, in Spanish, not to immediately repeal President Obama’s executive order preventing deportation of undocumented immigrants who came to the United States as children.

“Ted Cruz is telling lies,” Rubio responded, listing a series of instances in which he said Cruz had fibbed.

“I don’t know how he knows what I said on Univision. He doesn’t speak Spanish,” Rubio said, drawing from Cruz, who is conversant but not fluent in Spanish, a challenge in Spanish to debate in that language.

The circular firing squad left two candidates largely unscathed: neurosurgeon Ben Carson and Ohio Gov. John Kasich.

Carson, who has fallen out of contention in the race, did not capitalize on the opportunity. In fact, he delivered perhaps his oddest debate performance. He even attributed a statement to Josef Stalin that, it turns out, the Soviet leader never made. Responding to Democrats, who he said paint rich people as “evil,” Carson said “the evil government” is the problem.

Kasich, who also drew little criticism, went for an upbeat, at times folksy, tone. He pledged to reduce partisan battles and appeal to Democrats, while faulting his GOP competitors for their brawling.

“We’re fixing to lose the election to Hillary Clinton if we don’t stop this,” Kasich said.