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The Romney campaign used proxies to rebut Mr. Gingrich on Sunday, issuing several statements from supporters defending the former governor’s record and character. Former Minnesota Gov. Tim Pawlenty said Mr. Gingrich’s attacks were “over the line.”

“I have spent a lot of time with Mitt Romney, and I can tell you with zero hesitation that he is a man of flawless character,” Mr. Pawlenty said.

Another missive from the Romney camp quoted Virginia Gov. Bob McDonnell as saying he was “very disappointed to hear Speaker Gingrich make comments today that impugned Gov. Romney’s character.”

Mr. Gingrich collected the weekend endorsement of Herman Cain, a tea party favorite and former presidential hopeful whose White House effort derailed amid sexual harassment allegations.

“Speaker Gingrich is not afraid of bold ideas,” Mr. Cain said.

Former Texas Gov. Rick Perry endorsed Mr. Gingrich when he bowed out of the race in South Carolina.

The Cain endorsement, while not unexpected, comes at an opportune time for Mr. Gingrich. A win in Florida would do wonders to boost his national image and a campaign war chest much smaller than Mr. Romney‘s.

Meanwhile on Sunday, Mr. Santorum stayed home in Philadelphia to be with his hospitalized daughter and is canceling campaign stops in Florida. His 3-year-old, Bella, has a potentially fatal genetic condition known as Trisomy 18.

Santorum spokesman Hogan Gidley said the candidate hopes to return to a campaign schedule soon. Mr. Santorum also canceled his appearance on NBC’s “Meet the Press.”

This article is based in part on wire service reports.