“Governor Romney will not be able to hide behind negative ads,” Mr. Gingrich said on Fox News’s “Sean Hannity Show.” He added, “People will go, ‘Oh yes, that’s not somebody I want to be the Republican nominee.’ “

Jon M. Huntsman Jr., a former Utah governor, also took aim at Mr. Romney at an event Thursday night as he tried to jump-start his struggling campaign.

“The establishment is teeing up Mr. Romney as their choice,” said Mr. Huntsman, who received the endorsement of The Boston Globe on Thursday. “The people of New Hampshire will not be told for whom to vote. The people of New Hampshire do not want a coronation.”

The Boston Globe, which is owned by The New York Times, said that “while Romney proceeds cautiously, strategically, trying to appease enough constituencies to get himself the nomination, Huntsman has been bold.”

The paper added that Mr. Huntsman “would be the best candidate to seize this moment in G.O.P. history, and the best-prepared to be president.”

At an early-morning rally in South Carolina on Friday, Mr. Romney did not respond to the attacks against him. But John H. Sununu, a former New Hampshire governor who backs Mr. Romney’s presidential campaign, fired back during a Fox News interview Friday morning.

Mr. Sununu challenged Mr. Gingrich’s claim about abortion funding, calling that charge “wrong” and saying that “Mr. Gingrich has a little difficulty with the truth.”