President Obama is receiving both praise and criticism for promising not to prosecute CIA interrogators who followed the Justice Department’s perverse legal advice. But Obama’s decision may be less consequential than it seems. Congress already has anticipated the possibility of prosecution and has erected a significant barrier to it.

In the 2005 Detainee Treatment Act Congress provided as follows (it's worth wading through the legalese):

"In any civil action or criminal prosecution against an officer, employee, member of the Armed Forces, or other agent of the United States Government who is a United States person, arising out of the officer, employee, member of the Armed Forces, or other agent's engaging in specific operational practices, that involve detention and interrogation of aliens who the President or his designees have determined are believed to be engaged in or associated with international terrorist activity that poses a serious, continuing threat to the United States, its interests, or its allies, and that were officially authorized and determined to be lawful at the time that they were conducted, it shall be a defense that such officer, employee, member of the Armed Forces, or other agent did not know that the practices were unlawful and a person of ordinary sense and understanding would not know the practices were unlawful. Good faith reliance on advice of counsel should be an important factor, among others, to consider in assessing whether a person of ordinary sense and understanding would have known the practices to be unlawful. "

But wait -- there’s more! The DTA also says that the government "may provide or employ counsel, and pay counsel fees, court costs, bail, and other expenses" for interrogators."

In 2006 Congress passed the Military Commissions Act, which preserved legal protection for interrogators -- indeed, strengthened it by requiring, instead of just permitting, legal aid for interrogators. The Supreme Court found fault with the act for other reasons, but it didn’t object to protection for interrogators.

Granted, interrogators haven’t received total immunity. But Congress has erected a high hurdle for prosecutors to clear even if they do a better job than the Justice Department team in the Ted Stevens case. Obama’s "look forward, not backwards" mantra also reflects Congress’ attitude – and probably a jury’s as well.