(CNN) -- With GOP presidential front-runner Mitt Romney feeling comfortable enough to campaign in South Carolina, Newt Gingrich and Rick Santorum on Thursday scoured New Hampshire for votes and hammered away at each other's congressional record.
Gingrich, who got a boost from the state's top newspaper, knocked Santorum's role in Congress, suggesting the former Pennsylvania senator was a "junior partner" in the 1990s Republican revolution in Washington.
"He clearly in historical experience would have been the junior partner," Gingrich said, reminding voters which Republican was really behind the Contract With America.
Santorum noted his role in the "Gang of Seven," a group of freshman Republican lawmakers who exposed a scandal at the House bank in the early 1990s, before Gingrich rose to power as speaker.
"I was no junior partner in that. Newt was not involved in that revolution when it came to the corruption and the scandals. He sat on the sidelines," Santorum said.
Romney faced a fresh round of conservative criticism when a newspaper resurrected claims that the former Massachusetts governor helped pave the way for President Barack Obama's health-care reforms.
"Gingrich's record of conservative accomplishment is unparalleled and his beliefs and vision are passionate and clear," wrote Joe McQuaid, publisher of the New Hampshire Union Leader. Romney, in contrast, was "governor of the most liberal state in the country and managed to beat Obama at delivering Obamacare."
Conservatives must rally around the former House speaker "or face the very real prospect of having Barack Obama walk all over" Romney, McQuaid argued.
Former Utah Gov. Jon Huntsman, meanwhile, won the endorsement of the Boston Globe, which said only he and Romney were "truly presidential."
"While Romney proceeds cautiously, strategically, trying to appease enough constituencies to get himself the nomination, Huntsman has been bold," the Globe's editorial said. "Rather than merely sketch out policies, he articulates goals and ideals. The priorities he would set for the country, from leading the world in renewable energy to retooling education and immigration policies to help American high-tech industries, are farsighted."
Gingrich, stumping for votes in Plymouth, tried to distinguish himself from Romney by telling supporters that "there is a very big difference in our two sets of values. I don't believe a Massachusetts moderate is in a very good position to debate Barack Obama, and I think it would be very hard to win the general election because I think it just blurs everything."
Romney, campaigning in nearby Salem, continued his strategy of looking ahead to the general election, blasting Obama for appointing "labor stooges" to the National Labor Relations Board -- a frequent target of Republicans who accuse it of a pro-union bias.
Obama recently placed three new members on the panel while circumventing the Senate confirmation process, citing a right to do so through recess appointments while the Senate is not in session.
"This president has engaged and is engaging in crony capitalism," Romney asserted during a New Hampshire town hall meeting with Sen. John McCain, R-Arizona. "It is happening with the National Labor Relations Board, where he is paying back big unions that helped his campaign."
McCain endorsed Romney on Wednesday, one day after the latter's razor-thin victory in the Iowa caucuses. Romney waged a tough primary campaign in 2008 against McCain, the party's eventual presidential nominee that year.
McCain traveled Thursday with Romney to Charleston, South Carolina. The senator attacked Santorum's record of securing earmarks.
"Earmark spending is the gateway to corruption, and that was practiced when Republicans were in the majority," McCain said, flanked by Romney and South Carolina Gov. Nikki Haley, Romney's leading backer in the Palmetto State.
Santorum has come under fire from his GOP foes for his unapologetic defense of the earmarking process, which he says is simply a power granted to Congress under the Constitution.
Santorum will officially purchase a major ad buy in South Carolina on Friday, CNN has learned.
The former senator tangled with proponents of same-sex marriage at a convention of college Republicans in Concord, New Hampshire.
"Are we saying everybody has the right to marry?" Santorum asked the crowd.
"Yes, yes," shouted several members in the crowd.
Santorum later equated same sex marriage with polygamy.
Huntsman, meanwhile, touted poll results showing he is running ahead of Gingrich in the state and predicted his decision to skip Iowa and focus on New Hampshire would pay off.
"We're doing to do well. We're going to exceed market expectations," the candidate told CNN's "John King, USA."
Huntsman earlier said Santorum's emphasis on grass-roots campaigning in Iowa led to him coming within a hair's breadth of beating Romney, and Huntsman's efforts would produce similar results.
For his part, Santorum is trying to capitalize on the momentum from his late surge in Iowa, where he came within eight votes of beating Romney. But his sudden visibility has put him in the crosshairs of his opponents and led to more scrutiny from reporters.
The heads of both the NAACP and the National Urban League blasted Santorum this week after he was reported to have told an Iowa audience, "I don't want to make black people's lives better by giving them someone's money. I want to give them the opportunity to go out and earn the money."
The officials said Santorum was "singling out" African-Americans as poor.
Santorum said Wednesday that he didn't recall saying "black," telling CNN's "John King USA" that "It was probably a tongue-tied moment as opposed to something that was deliberate."
"I started to say a word and sort of mumbled it and changed my thought. I don't recall saying black. No one in that audience heard me say that," he said.
Texas Rep. Ron Paul, meanwhile, used his close third-place showing in Iowa as fuel for his libertarian anti-establishment message, while Texas Gov. Rick Perry said he would press on to "places where they have actual primaries" after his fifth-place finish Tuesday night.
Rep. Michele Bachmann of Minnesota dropped out Wednesday after coming sixth in Iowa.
Next Tuesday's New Hampshire primary appears to be Romney's to lose.
Romney benefits from a virtual favorite-son status there, not to mention a significant advantage in terms of campaign cash and organization. He is far ahead in most recent statewide polling and can now boast of a first-place finish in the Iowa caucuses, albeit by a razor-thin margin.
Meanwhile, after taking a night to rethink his campaign, Perry announced to supporters via Twitter that he would stay in despite his 10% showing in Iowa.
He told reporters later that he would take part in two debates in New Hampshire and campaign in South Carolina, which holds the first Southern primary January 21.
Of the 25 pledged delegates at stake in Iowa, CNN has estimated that Romney, Santorum and Paul will each win seven, with Gingrich and Perry picking up two apiece.
It will take 1,144 delegates to capture the nomination at the Republican National Convention in Tampa, Florida, this summer.
CNN's Alan Silverleib, Peter Hamby, John Helton, Gabriella Schwarz, Shawna Shepherd, Paul Steinhauser, Shannon Travis, Jim Acosta, Jessica Yellin, Jason Hanna and Keating Holland contributed to this report