Obama advisers and other Democrats see a Santorum whose record, writings and statements, particularly on social issues, will be used to portray him as far too conservative for many voters. His record, they say, could make Santorum anathema to suburban swing voters, especially women. That view is shared by some Republicans and independent analysts.

“They [Democrats] would brutalize him on social and cultural issues and present him as so far out of the mainstream as to be radical,” said G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin & Marshall College and a leading pollster in Pennsylvania. “The analogy would be Barry Goldwater” — the 1964 GOP nominee who suffered a landslide defeat.

Santorum’s advisers recognize that he has entered a new phase in his campaign, and they see the obstacles ahead. They argue that a full and fair reading of his record reveals a more attractive profile of the former senator. But they acknowledge it is up to Santorum and his campaign to explain that record and allay concerns about his ability to run competitively in November.

“There will be people — Romney and the Democrats — who will try to distort these things,” said John Brabender, Santorum’s longtime political adviser. “It’s the responsibility of our campaign to show what the senator’s record really is. We are confident that once that happens, people will understand that the senator is extremely reasonable.”

The first tests will come over the next 10 days, as Santorum attempts to leverage his new prominence against Romney in primaries in Arizona and especially Michigan, and then on Super Tuesday, March 6.

Romney and the super PAC backing his campaign have begun to attack Santorum — though not for being too conservative. That may be too risky for a candidate whose conservative credentials are already considered suspect by many on the right.

Instead, they say Santorum strayed from his conservative moorings whenever it was politically convenient to do so. He backed earmarks for projects in his state and district. He voted, as did many in his party, to raise the debt ceiling repeatedly. He backed higher spending to pay for prescription drug benefits under Medicare. He was cozy with labor unions, an important constituency in Pennsylvania.

Those issues likely will be prime topics at Wednesday’s GOP debate in Arizona, and Santorum advisers say they are eager to take on Romney and his attacks in that forum. Romney, they say, is the GOP candidate with questionable conservative credentials, and they are determined to win that definitional battle.