Rick Perry has gone from the piñata to the punch line.

Three debates into the Perry for president campaign, the governor vanished for much of the night Thursday, except when Mitt Romney was delivering a critical reading of Perry's book.

With his hard-charging campaign stuck in neutral and Romney gaining ground in South Carolina, Perry had trouble getting attention in a stiff debate with more candidates than a Big 12 expansion rumor.

When Perry was on camera, the scene usually looked less like a political debate than a perp walk.

Both Romney and Rick Santorum shook accusing fingers at Perry over Social Security and illegal immigration, stirring viewers in the Fox News Channel/Google debate to search "Who is Rick Santorum?"

Santorum drew cheers for challenging Perry about Texas' law allowing illegal immigrants to pay in-state college tuition.

"Why should they be given preferential treatment?" Santorum asked, calling Perry "soft."

Perry had already played the guilt card, saying if you don't educate those children, "you have no heart." But he responded defiantly, "Have you ever been to the border?"

Romney and Perry had already made fun of each other, with Romney saying that if Perry no longer believes what he wrote in Fed Up! about Social Security, "then you better find that Rick Perry and get him to stop saying that."

Then Perry fumbled a question about Pakistan by rambling about India, proving only that he knows they're adjacent, even though neither is a candidate to join the Big 12.

The Pakistan answer was Perry's worst, wrote political science professor Jeffrey Berry of Tufts University near Boston.

"He demonstrated little knowledge of foreign affairs," Berry wrote.

Otherwise, he called Perry "reasonable."

Texas Christian University political science professor Adam Schiffer wrote by e-mail that Perry's worst problem is an immigration position "too complex for sound bites."

"I thought his answer was strong," Schiffer wrote. "I don't know if the base will agree."

It was too late when Perry began questioning "which Mitt Romney" he's running against.