MYRTLE BEACH, South Carolina (AP) ― Mitt Romney’s Republican rivals attacked his record as a venture capitalist Monday night in the first of two debates before a pivotal weekend primary in South Carolina, where a Romney victory could seal his lock on the Republican nomination to challenge President Barack Obama in the November general election.

The president ― weighed down by a struggling American economy ― is seen as vulnerable in his quest for a second White House term. Relentlessly high unemployment, massive federal debt and millions of home mortgage foreclosures persist as the economy makes a laggardly recovery from the Great Recession of 2007-2009. Of all issues facing the United States, voters say repairing the economy is foremost.

The debate unfolded hours after moderate former Utah Gov. Jon Huntsman withdrew from the race and endorsed Romney.

That withdrawal only raised the stakes of the debate ― and one on Thursday night. In the debate, feisty from the outset, Newt Gingrich, Rick Santorum and Rick Perry sought to knock Romney off stride while generally being careful to wrap their criticism in anti-Obama rhetoric.

“We need to satisfy the country that whoever we nominate has a record that can stand up to Barack Obama in a very effective way,” said Gingrich.

Polls show Romney, the former Massachusetts governor, as the clear favorite in conservative South Carolina despite the mistrust or ambivalence of Republican voters who are unhappy with Romney’s past stands on social issues like abortion. Gingrich has virtually conceded that a victory for Romney in the first-in-the-South primary in South Carolina would assure his nomination.

Gingrich and Perry led the assault against Romney’s record at Bain Capital, a venture capital firm that bought companies and sought to remake them into more competitive enterprises.

“There was a pattern in some companies ... of leaving them with enormous debt and then within a year or two or three having them go broke,” Gingrich said. “I think that’s something he ought to answer.”

Perry referred to a steel mill in South Carolina where, he said, “Bain swept in, they picked that company over and a lot of people lost jobs there.” “I’m proud of my record,” the former Massachusetts governor responded, but he avoided an answer on making his tax returns public.

Romney said that the steel industry was battered by unfair competition from China. As for other firms, he said, “Four of the companies that we invested in ... ended up today having some 120,000 jobs.

“Some of the businesses we invested in were not successful and lost jobs,” he said, but he offered no specifics.

Perry challenged Romney, a multimillionaire, to release his income tax returns. The Texas governor said he has already done so, adding he believes Gingrich will do likewise later in the week.

Romney grudgingly said Monday night he might release his income tax returns this spring.

“I have nothing in them that suggests there’s any problem and I’m happy to do so,” he said. “I sort of feel like we’re showing a lot of exposure at this point,” he added.

Afterward, Gingrich said that wasn’t good enough. “If there’s nothing there, why is he waiting till April?” the former House speaker told reporters.

In South Carolina, a state with a heavy military presence, the tone turned muscular at times.

Gingrich drew strong applause when he referred to a 19th century U.S. president: “Andrew Jackson had a pretty clear idea about America’s enemies. Kill them.”

Perry also won favor from the crowd when he said the Obama administration had overreacted in its criticism of the Marines who were videotaped urinating on the corpses of Taliban fighters in Afghanistan.

Early this month, Romney won the leadoff Iowa caucus preference poll by just eight votes over Santorum, the former Pennsylvania senator, but went on 10 days later to handily win the primary election in New Hampshire, where he maintains a vacation home.

Santorum, Gingrich, the former speaker of the House of Representatives, and Perry, the Texas governor, have all had a time in the limelight as the biggest threat to Romney, but all also have faded to also-ran status as Republicans appear to be coalescing around Romney.

Texas congressman Ron Paul, a strict libertarian who favors small government, has held steady through the first months of the campaign, but manages on average to poll only in the teens.

After the Monday debate, Republican candidates face a packed week of campaign events and one more nationally televised debate on Thursday. In the past three decades, no Republican has won the party’s presidential nomination without carrying South Carolina.