At a campaign appearance here on Saturday morning, Mr. Santorum described the “president’s agenda” as being “not about you. It’s not about your quality of life. It’s not about your job.”

“It’s about some phony ideal, some phony theology. Oh, not a theology based on the Bible, a different theology. But no less a theology,” Mr. Santorum said, to wide applause. …

Mr. Santorum’s statement brought a swift rebuke from the Obama re-election campaign, which in the past has tended to focus more on attacks by Mitt Romney. Their quick attention to Mr. Santorum’s comments may be an indication that Democrats believe Mr. Santorum’s momentum now means he stands a decent chance of defeating Mr. Romney for the Republican nomination and facing Mr. Obama in the general election this fall.