WASHINGTON -- Former Sen. Rick Santorum couldn't suppress his laughter Wednesday morning when reminded that he had once declared Mitt Romney to be the single worst Republican candidate to run against President Barack Obama on the issue of health care.

The Republican National Committee tapped Santorum to host a conference call attacking the Obama administration's new welfare waiver policy. But the question and answer session quickly turned back to that heated moment between the two, which took place during the Republican primary.

Andrea Saul, a top spokeswoman for Romney, stoked conservative fears on Wednesday by touting the health care law the former governor had passed in Massachusetts during an appearance on Fox News. Reporters wanted to know if Santorum felt a sense of vindication.

"I didn't see the show so I'm not going to comment on that," he said of Saul's remark that a woman, highlighted in a recent ad from a pro-Obama super PAC, would have had health insurance to help pay for her cancer had she lived in Massachusetts.

But even as Santorum ducked the issue, it seemed clear that his heart wasn't entirely in it. He let out a noticeable laugh as he offered a defense against the notion that Saul had given Obama a gift by speaking positively about the universal insurance model that Romney pioneered and the president adopted.

"All I can say is that [laughter] Governor Romney is going to be a far superior candidate [laughter] on the issue of health care than Barack Obama," said Santorum. "And Governor Romney has been clear, number one, he would fight for the repeal of Obamacare. He said that during the campaign."

"The differences between Governor Romney and me in the primary really fall to the wayside when it comes to the differences between the Republican nominee, Governor Romney, and Barack Obama," Santorum added.

Amanda Terkel contributed reporting.

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