The key word being “prosecution.” That’s his out. No journalist has been prosecuted.
Yes, he'll smugly try to pull that. "Prosecuted," past tense, of course, is a very different thing than "potential prosecution", which were his words in congressional testimony.
The Catch-22 for him is that pesky sworn affidavit to the judge requesting permission for the records seizure. Would the judge have granted that if Holder had said that prosecuting Rosen--this target of their investigation, this danger to national security and a real flight risk--is not something he would ever even think of?
So, which is it, Holder? You either lied to congress or grossly misled the court to get your Genuine, Official Trample the Constitution Permit. Pick your poison.