The Republican presidential candidates squared off in a South Carolina debate that featured nasty personal attacks and accusations of lying that were ramped up beyond anything previous in the campaign, perhaps signaling the higher stakes as the GOP prepares for this state’s primary.

Donald Trump, in an unconventional step for a Republican hopeful, harshly criticized the last GOP president, George W. Bush, for failing to prevent the 9/11 attacks and launching the subsequent invasion of Iraq. But that was just the beginning.

Sen. Marco Rubio (R-Fla.) and Trump repeatedly called Sen. Ted Cruz (R-Texas) a liar. Cruz blasted Rubio on immigration and spoke Spanish to taunt Rubio — after Rubio accused him of not being able to speak the language. Trump called Cruz a “nasty guy” — prompting Cruz to say Trump calls a rival a liar only when Trump’s “liberal” record is highlighted.

Ohio Gov. John Kasich sought to play the adult on the stage who could win “blue collar Democrats” in key states. He said all the personal attacks could cripple the Republican nominee in the fall.

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

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The sharp exchanges were part of the last debate before the six remaining candidates vie in South Carolina’s crucial GOP primary next Saturday. Promoted as the “first in the South” primary, it marks a shift of the campaign focus from New Hampshire to more conservative states. And South Carolina will help shape the focus for the March 1 “Super Tuesday” primaries.

The most heated exchanges came between former Florida Gov. Jeb Bush and Trump, like they seemingly always do in these Republican debates. Trump harshly criticized former President George W. Bush for invading Iraq, which he called “a big, fat mistake.”

“George Bush made a mistake. Everyone makes mistakes but that was a beauty,” Trump said at the Greenville, South Carolina, forum. “They lied. They said there were weapons of mass destruction. There were none and they knew there were none.”

Jeb Bush contended that his brother “kept us safe” after the 9/11 attacks. But Trump came back with another volley.

“The World Trade Center came down when under the reign of George W. Bush! Remember that!” Trump shouted.

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When he wasn’t sparring with Trump, Bush tried to portray Cruz and Rubio as freshman senators lacking executive experience to govern. To that point, when moderators asked Rubio for an example of being tested in a crisis, he offered his vote against invading Syria.

Kasich said of the Trump-Bush bickering: “This is crazy. This is nuts.”

The governor, portraying himself as the most electable Republican, warned voters that his rivals wouldn’t be able carry “blue collar Democrats.”

Retired neurosurgeon Ben Carson said that his lack of political experience wouldn’t be a handicap, and that judgment was more important. And he chided the others’ food fight.

“Is that what you want? What we just saw?” Carson said, looking at the audience.

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The night started with most of the GOP hopefuls saying that because it is an election year, President Barack Obama should give up his power to nominate a successor to U.S. Supreme Court Justice Antonin Scalia, who died Saturday.

CBS moderators pointed out that Justice Anthony Kennedy, a Reagan nominee, was confirmed to the court in 1988, an election year. That prompted Bush to say that if Obama nominated someone, it should be a “consensus” candidate. Trump acknowledged he would nominate someone if he were in the same situation. He urged Republicans in the Senate to “delay, delay, delay” any Obama nominee until a new president is sworn in.

Cruz, seen as a favorite among evangelicals, used the issue to say: “We are one justice away from a Supreme Court that will strike down every abortion restriction” that’s been implemented by the states, and also said the court could strike down Second Amendment rights.

Rubio said the “Constitution is not a living and breathing document” and that it should be applied strictly as it is written. He was the lone candidate, in his closing statement, to invoke his opposition to same-sex marriage.