I haven't heard it yet - I was at a rehearsal this morning during the broadcast, and my husband told me about it. I'll have to download today's podcast. But what a WONDERFUL term for it! I Googled the phrase and find it's used quite a lot and has turned up on DailyKos and in William Safire columns. The latest relevant use, actually about Awful Alberto, is a very similar post last Wednesday in Jeff Weintraub's blog, So It Goes. It's also called the "past exonerative" and "past passive exonerative."
The So It Goes post ends with a summary that is better than I could have written:
Politicians who use it think they're dousing a fire. They should all remember the teachings of their composition teachers. Because when the rest of us hear "mistakes were made," we know the fire has only begun to burn.