Assuming President Obama is the genius that his supporters believe him to be, he must know this (and it is probably why he has "outsourced" the ultimate decision to the Justice Department). And so his willingness to signal the possibility of such prosecutions is little more than throwing a bone to the most rabid of his left-wing supporters.
Given the damage that his "door-opening" will do to national security -- the chilling effect it will have on government officials, who will now have to fear that something declared legal today will get them prosecuted tomorrow -- it's quite remarkable that the president would go so far for nothing but political reasons. Remarkable, and sad.
In any case, if any such prosecutions go forward, they should spark wholesale resignations at the CIA and elsewhere. How can officials be expected to offer their best judgment when they know it may result in their prosecution later -- and who can blame them for doing little but covering their behinds (something that happens enough in government as it is)?