(J. Scott Applewhite/Associated Press)

To which detractors say: impossible.

As was the case with his March hearing on the radicalization of Muslim Americans, the detractors are accusing the congressman of scare-mongering. They see this week’s hearing as being rooted in no more than Islamophobia.

But as King told Fox News on Monday, there’s “absolutely nothing wrong” with inmates converting to Islam. “The problem,” he said, “is when you get radical Muslims. You get radical chaplains who then radicalize them and turn them toward terrorism or turn them toward violence.”

King is hardly the first person to voice of concern about the radicalization of Muslims in American prisons. FBI Director Robert Mueller told a Senate committee six years ago that prisons were “fertile ground” for Islamic extremists. Even before that, in 2003, Sen. Charles Schumer, the Democrat of New York, expressed concern that U.S. inmates were being recruited by followers of the ultraconservative brand of Islam known as Wahhabism.

But for critics, the issue is that the radicalization of American Muslim inmates should not be seen apart from the radicalization of inmates by other groups. And experts note that in U.S. prisons, for generations, there’s been plenty of radicalization to go around, from the Aryan Brotherhood to the Latin Kings to the Black Liberation Army.

“There have been periods through history where different religious groups have attempted to gain converts in prison systems,” said Arnett Gaston, an adjunct professor in criminology and criminal justice at the University of Maryland. Today, “there is a threat, but it is not indigenous or specific to Muslims.”

Gaston is a former commanding officer at Rikers Island, where he had responsibility for 18,000 inmates and 11,000 staff. In his 51 years in the criminal justice system, he said, he has seen no evidence that Muslim American inmates pose a greater threat than other groups.

Indeed, a 2010 report by the nonpartisan Congressional Research Service concluded that prisons, “seen by some as potential hotbeds of radicalization, have not played a large role in producing homegrown terrorists.”

At the same time, experts say, the path to radicalization can be a complicated one, making it difficult to say with certainty when incarceration played a role in someone’s ideological evolution.

“This is not a straight-forward problem. This is a complete, criminological problem,” said Mark S. Hamm, a professor of criminology at Indiana State University.

Hamm, who had been briefing congressional staff ahead of this week’s hearing, said he has scoured prison memoir literature, databases and foreign research to try to find case studies in which an inmate’s prison stretch led to a process of radicalization and then to plans for terrorist attacks on Western targets. He calls the cases he’s found the “spectacular few.”

“If you had to go to the Smoky Mountains and identify and locate and kill one mosquito in July, that’s the analogy I try to use here,” he said.

But as Hamm said, even if inmates embracing radical Islam represent an infinitesimal part of the prison population, a single one could be capable of committing horrific acts of terrorism.

“I do think it’s an issue that needs more study,” he said.