(CNN) -- GOP frontrunner Mitt Romney's campaign stepped up its criticism of conservative challenger Rick Santorum on Friday, continuing to hit the former Pennsylvania senator on his spending record while in Congress.
For his part, Santorum was slated to hold three "Faith, Family and Freedom" town hall meetings in New Hampshire, now four days from its first-in-the-nation primary.
In addition, Newt Gingrich, Jon Huntsman and Ron Paul had events scheduled in the state.
Romney holds a large lead in New Hampshire in most polls, which has resulted in high expectations for his performance next Tuesday. The other candidates appear to be scrambling for a second-place finish that could provide them with momentum heading into the January 21 South Carolina primary.
Catching Romney in South Carolina, however, may prove to be a slog for his Republican rivals. A CNN/Time/ORC International poll released Friday shows 37% of likely GOP Palmetto State primary voters backing the former Massachusetts governor, compared with 19% for Santorum, 18% for Gingrich, and 12% for Texas Rep. Ron Paul.
The survey's sampling error is plus-or-minus 4.5 points.
Stumping Friday morning with Romney in South Carolina, Sen. John McCain or Arizona blasted Santorum's defense of earmarks -- federal spending designated for specific projects in individual states or districts. Tea party activists and other conservatives frequently cite earmarks as prime examples of what they see as out-of-control spending in Washington.
"Earmarks are a gateway to corruption," McCain said. "When Rick Santorum sponsored earmark after earmark, I went down to the floor and fought against those. ... I guarantee you (Romney) will fight against it time after time after time, and we will stop the waste."
Romney is "going to know that spending matters," declared South Carolina Gov. Nikki Haley, another supporter of the former governor. "That's why I know he is right as the president."
Santorum responded that the federal government's big problem with spending is entitlement programs, not earmarks. "There is where the big, unfunded liabilities are," he said. "Candidly, this is John McCain trying to put his imprimatur on the Republican conservative movement."
Santorum recently told CNN it's important, as a member of Congress, to "fight to make sure you get your fair share." Santorum helped secure at least $1 billion in earmarks for Pennsylvania while in Congress, according to the nonpartisan group Taxpayers for Common Sense.
On Thursday, Gingrich and Santorum -- who rode a late surge to a close second-place finish in Iowa -- sniped at each other's conservative credentials and congressional records.
Gingrich also knocked Santorum's role in Congress, suggesting he was a lesser player in the 1990s Republican revolution in Washington.
"He clearly, in historical experience, would have been the junior partner," the former House speaker said, reminding voters of his own role in the 1994 Contract With America.
Santorum, in turn, noted his role in the "Gang of Seven," a group of freshman GOP lawmakers who exposed a scandal at the House bank in the early 1990s, before Gingrich became speaker.
"I was no junior partner in that," Santorum said. "Newt was not involved in that revolution when it came to the corruption and the scandals. He sat on the sidelines."
Romney, meanwhile, 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 said.
Huntsman, who has focused almost exclusively on New Hampshire for months, won the endorsement Thursday of the Boston Globe, a hometown paper for Romney that has often had a contentious relationship with the former Bay State governor.
"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."
Asked about his lackluster 1% polling draw in South Carolina, Huntsman told CNN that that need not prove fatal. "We don't have to win," he said. "We have to beat market expectations" in order to gain momentum and raise money.
Romney senior strategist Eric Fehrnstrom brushed off the Globe's endorsement, noting that "Boston is a two-newspaper town, and the Globe has a liberal editorial page." Fehrnstrom touted Romney's endorsement by the smaller Boston Herald, which generally has a more conservative outlook.
Gingrich tried to distinguish himself from Romney Thursday by telling supporters in Plymouth, New Hampshire, 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 himself tried to keep the focus on Obama, blasting the president Thursday for appointing "labor stooges" to the National Labor Relations Board -- which Republicans have accused of having a pro-union bias.
Obama recently placed three new members -- two Democrats and a Republican -- 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. "It is happening with the National Labor Relations Board, where he is paying back big unions that helped his campaign."
CNN's Alan Silverleib and Dana Bash contributed to this report