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Mr. Adams said he doesn’t buy Mr. Santorum’s explanation about getting a commitment from Mr. Specter on judicial nominations, because Sen. Jon Kyl of Arizona, a conservative, was next in line in seniority to get the chairmanship if Mr. Specter did not. He noted that Mr. Santorum also endorsed Mr. Specter’s long-shot bid for president in 1996.

“I just think Rick’s allegiance to Arlen Specter seemed to have trumped all other allegiances, even pro-life,” said Mr. Adams, whose tea party group has endorsed Mr. Romney.

Some conservatives say the episode also contributed to Mr. Santorum’s loss in 2006 to Democrat Bob Casey. It was a Democratic year, but they say conservatives’ enthusiasm for Mr. Santorum had eroded.

“I do think it hurt him,” said Mr. Adams. “People by that point couldn’t stomach it any longer.”

In the 2004 primary, conservatives were further angered by Mr. Santorum’s “nastiness” toward Mr. Toomey, said Ryan Shafik of Harrisburg, Pa., a political strategist who once worked as an intern for Mr. Santorum and later worked on Mr. Toomey’s campaigns.

“He went to an extra level to really hurt Pat,” Mr. Shafik said. “That’s what really angered activists.”