Donald Trump got into it with pretty much every other candidate at the Feb. 13 CBS News GOP debate. (Peter Stevenson/The Washington Post)

Donald Trump got into it with pretty much every other candidate at the Feb. 13 CBS News GOP debate. (Peter Stevenson/The Washington Post)

In an election that Republicans have long seen as a chance to put forward new stars with a fresh and broadly appealing conservative vision, the GOP is instead at risk of tearing itself apart over its past as it heads into the thick of the primary season.

A day after a debate marked by a series of personal, petty exchanges — and a day before former president George W. Bush was set to make a high-profile return to the national scene — Republicans were grappling with their core beliefs on a host of issues, as well as the image they were broadcasting to the country.

The infighting was ignited at the debate Saturday night by front-runner Donald Trump, who was unrelenting in his criticism of both how well the 43rd president kept America safe before and after the Sept. 11, 2001, attacks and of the hawkish Republican worldview in general.

The foreign policy fracas is only the latest row among 2016 candidates over many of the basic tenets that have guided Republican and conservative thinking since the Reagan years, from free trade to the extent to which the federal government should be involved in providing health care for its poorest citizens.

Trump reiterated threats to use tariffs on imported goods to punish corporations that leave the United States, while Ohio Gov. John Kasich defended his decision to accept an expansion of Medicaid in his state as a humane step in line with conservative goals.

1 of 25 Full Screen Autoplay Close Skip Ad × Republican presidential candidates clash during CBS News debate in South Carolina View Photos The six remaining GOP candidates differed sharply on U.S. foreign policy just hours after learning of the death of Supreme Court Justice Antonin Scalia. Caption The six remaining GOP candidates differed sharply on U.S. foreign policy just hours after learning of the death of Supreme Court Justice Antonin Scalia. Feb. 13, 2016 Ohio Gov. John Kasich, left, Jeb Bush, Sen. Ted Cruz (Tex.), Donald Trump, Sen. Marco Rubio (Fla.) and Ben Carson take the stage beneath an image of Supreme Court Justice Antonin Scalia, who died earlier in the day, for the Republican debate in Greenville, S.C. Erik S. Lesser/European Pressphoto Agency Buy Photo Wait 1 second to continue.

The increasingly harsh discussions of these and other issues amount to an existential crisis within the Republican Party and reflect the growing influence of non-ideological, populist voters who have flocked in particular to Trump’s nationalist “Make America Great Again” message.

Trump was defiant and unapologetic Sunday, saying that he is a truth-teller and that the majority of Americans — weary of war, alienated by the political class and thirsting for a populist revival — would heed his call.

“The war in Iraq has been a disaster,” Trump said Sunday on CBS’s “Face the Nation.” “It started the chain of events that leads now to the migration, maybe the destruction of Europe. [Bush] started the war in Iraq. Am I supposed to be a big fan?”

Todd Harris, a senior adviser to Sen. Marco Rubio of Florida, echoed the sentiment of many in the GOP when he said after the debate that Trump “was at war with the Republican Party.”

So far, at least, it is a war that many Republicans are willing to wage alongside Trump. Fresh off his commanding win in the New Hampshire primary, a new poll released Sunday by CBS News showed Trump surging here ahead of Saturday’s South Carolina primary. The survey showed Trump with the backing of 42 percent of Republican voters, more than double the support of his closest rival, Sen. Ted Cruz of Texas.

The poll was taken before the debate and the ensuing fallout, which many Republicans predicted would limit Trump’s appeal going forward.

Nevertheless, the coming weeks will test not only who is most popular in South Carolina but whether the ties that have bound the GOP for a generation will unravel entirely.

Jeb Bush poses for a photograph with his wife, Columba, after the Republican presidential debate Saturday night in Greenville, S.C. (John Bazemore/AP)

Sen. Lindsey O. Graham (S.C.), a supporter of Bush, said of Trump: “This man accused George W. Bush of being a liar and suggested he should be impeached. This man embraces [Russian President Vladimir] Putin as a friend. The market in the Republican primary for people who believe that Putin’s a good guy and W. is a liar is pretty damn small.”

As confident as the Republican establishment is that voters will eventually turn against Trump for his apostasies and controversies, there is little evidence that they will. Still, other contenders are making their most concerted effort yet to stop him here, even though many top party officials and financiers are remaining on the sidelines and previous attempts to take down Trump have attained little.

If the real estate magnate is able to win convincingly in South Carolina, he would enter the ­“Super Tuesday” states on March 1 with considerable strength and having endured a sustained assault. Despite the polls, Trump’s competitors and their allies view South Carolina as perhaps their best opportunity to slow or stop Trump’s march to the nomination.

Bush, the former Florida governor, hopes to capi­tal­ize on the argument over his brother’s legacy here, where polling suggests George W. Bush’s popularity is extremely high among Republicans. The Bush brothers will appear together at a rally Monday night in North Charleston, where Graham predicted the crowd would cheer so wildly that the Richter scale would break.

The escalating quarreling may increase the likelihood of a long, expensive and potentially futile effort to unite Republicans around the eventual nominee. The barbs at Saturday’s debate were ferocious and personal: Trump made fun of Bush’s mother and bickered with him over whether Bush had suggested that he would drop his pants and moon people (which he had); Rubio jabbed Cruz for not being fluent in Spanish; and they all seemed to call one another liars.

Pollster Frank Luntz, who for years has helped Republicans carefully calibrate their language to appeal to a broad range of voters, was aghast.

“If 10-year-old kids spoke to their teachers the way those candidates spoke to each other, those kids would be suspended,” he said. “There is no way that any independent observer can say the Republicans gained a single vote against the Democrats because of last night. If you’re honest and unbiased, the GOP lost votes last night.”

Kasich, who largely avoided the vitriol, warned during the debate and again Sunday morning that the nominee could emerge so bloodied that he might lose in the general election.

“It was like a demolition derby. . . . I think these debates are ridiculous. This is not a way to pick a president,” Kasich said Sunday on ABC’s “This Week.”

Ben Carson sounded a similar note. The retired neurosurgeon wrote in a fundraising email to supporters on Sunday: “Last night’s debate was ugly, vicious, and not worthy of the American people. There’s a reason that the first word in my campaign slogan is ‘heal,’ and last night it was there for everyone to see. The cancer of divisiveness is corroding our politics and the soul of our nation and if we don’t fix it, nothing else matters.”

On the debate stage, Trump blamed the Sept. 11, 2001, terrorist attacks in part on George W. Bush, and he accused Bush of lying to the American people by directing the 2003 invasion of Iraq despite knowing, according to Trump, that there were no weapons of mass destruction there.

Trump’s strident criticism reopened a wound that party leaders had hoped was in the past. Jeb Bush’s advisers and supporters scoffed and argued that — finally — Trump had done himself in.

“ ‘Bush lied, people died’ — that’s the Democrats’ refrain,” said former senator Norm Coleman (R-Minn.), a Bush backer. “It’s a bridge too far. What do they say? Jump the shark? 9/11, blaming Bush — that’s a kooky thing, that’s a conspiracy thing, that’s way out there.”

Jason Miller, a senior adviser to Cruz, said Trump’s comments about the Sept. 11 attacks were “completely out of step with the Republican base and most Americans overall. I think it will reverberate not just here in South Carolina but across the field for as long as this contest continues.”

The possible danger for Bush’s defenders is that though the family may be generally revered in some quarters of the party, its political standing is complicated. Embracing the Bush mantle, with its elite pedigree and associations with war, could prove problematic.

Trump and his team are confident that the hawkish mind-set that has defined Republican orthodoxy since the Cold War is now viewed suspiciously by grass-roots conservatives.

“He has been very clear on the foreign policy side that the Iraq war was a disaster. I think a lot of people agree with that,” said Corey Lewandowski, Trump’s campaign manager. “We lost thousands of lives and $5 trillion for what?”

As the candidates returned to the campaign trail, the mess they left behind on the stage of Greenville’s Peace Center had some party strategists wondering whether the damage may be politically irreparable.

“I saw assaults going on across the stage: Mr. Trump to Jeb, Jeb to Mr. Trump, Cruz to a lot of people, and on and on,” said John Weaver, Kasich’s chief adviser. “It was shameful all around, actually, and it’ll put us in a bind as a party.”