I don't want to agree with Tyler Cowen on the politics of torture prosecutions, but I think I actually do:
I believe that a full investigation would lead the U.S. public to, ultimately, side with torture, side with the torturers, and side against the prosecutors. That's why we can't proceed and Obama probably understands that. If another attack happened this would be all the more true.
Tyler notes that he agrees with the moral stance of those criticizing Obama's attitude towards prosecution. So do I. But insofar as Obama's opposition to torture prosecutions goes, I think it might be as much the calculation of an anti-torture pragmatist as the cowardice of a politician who'd prefer to move on. Right now, he's essentially assumed to have "won" the issue, and the American consensus is anti-torture. Opening up prosecutions -- which will inevitably see tough talking CIA agents swearing that sleep deprivation saved American lives -- could change that.
There are two counterarguments to this. One is the legal point eloquently offered by Glenn Greenwald, who simply says, "the notion that the law can and should be ignored whenever we think doing so would produce good results or would constitute good policy was the engine that drove Bush lawlessness."
Then there's the more instrumental counterargument. Prosecutions impact individual incentives rather than simply political incentives. Obama has won the argument only so long as he remains in office. A win at the polls is not a durable victory. It can be obviated by someone else winning at the polls. But there might be more rank-and-file resistance to torture, however, if future CIA agents looked back and realized that they could be vulnerable to prosecution once the politics changed. Safety in the moment would not imply safety across time periods. And you'd really only need one high-profile, successful prosecution to show that.