“The coordination that I felt at that debate the other night was pretty clear,” Mr. Santorum said in response to a question from the audience. “I felt like the messages were being slipped behind my chair.”

He concluded: “We need to go out and say we don’t need the Ron Paul faction and the moderate establishment teaming up to attack the real conservative in this race.”

Immediately after the debate on Wednesday night, Mr. Santorum said he was suspicious that the two may have been colluding. That prompted Stuart Stevens, a senior Romney adviser, to accuse the Santorum campaign of “whiny silliness” and to say that it was flailing in desperation.

The idea that the famously independent Mr. Paul would collude with anyone was absurd, Mr. Stevens said.

“The notion that Ron Paul would do anything but speak his mind is not an argument you can push very far,” Mr. Stevens said. “If ever there was an iconoclast who got up there and said what he believes, it’s Ron Paul.”

Tensions have been rising as the polls for the Republican presidential nomination have narrowed in Michigan in advance of Tuesday’s primary, which is viewed as a make-or-break moment for Mr. Romney. He and Mr. Santorum both have set aggressive schedules across the state in the closing days, and Mr. Paul is campaigning here, too. Newt Gingrich has opted out of Michigan and Arizona, and is instead campaigning on the West Coast. Mr. Santorum appeared Saturday afternoon in Tennessee, which holds its primary on Super Tuesday, March 6.

Mr. Santorum’s frustration spilled out during his speech in St. Clair Shores on Saturday morning. “It’s absolutely laughable for a liberal governor of Massachusetts to suggest that I am not conservative,” he told the crowd of about 150 people. “The man that provided the template for Obamacare, the man who supported the Wall Street bailouts. The man that said that he supported Romneycare. Oh, he wasn’t imposing any morning-after pills on the Catholic Church. ‘Oh, no, I didn’t do that.’ And he repeatedly gets up and says all these things that he didn’t do that he did do.”