"Reagan rejected Newt's ideas," the ad said.
ROF has also slowed Santorum by painting the former Pennsylvania senator as an unprincipled deal-maker and an outspoken champion of home-state spending projects known as earmarks.
"I'm very proud of all the earmarks I put in bills," Santorum is shown saying in one ad.
In Wisconsin, which holds its primary April 3, Restore our Future is spending $2.3 million on ads against Santorum, including one that begins and ends with a clip of him saying "I don't care what the unemployment rate's going to be. It doesn't matter to me."
Santorum made that remark at a campaign appearance earlier this month in Illinois. He later clarified his comment by saying his campaign was about freedom from an intrusive government, not just monthly jobless figures.
Collegio, the spokesman for American Crossroads, one of many independent groups that are expected to spend millions this year attacking Obama, said Romney and Republicans wouldn't be alone in running negative ads during the campaign.
"Obama will have a much harder time winning if it's a referendum on him and his administration. More than anything they want 2012 to be about their challenger," Collegio said. "And if that's Mitt Romney, it means (his former private equity company) Bain Capital, his net worth and other things they view as comprising Romney's negatives."
Ken Goldstein, of Kantar Media/Campaign Media Analysis Group, which tracks political advertising, said the TV ad strategy on both sides may bear little resemblance to how the Republican nominating contest has gone so far.
"People either love or hate Obama, and those in the middle, who are going to decide the 2012 election, haven't tuned in yet," Goldstein said. "Do you think they'll be moved more by ads or by realities like the economy?"
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