Second, lots of speculation on who flipped. Here is my completely invented guess: Karl Rove. Why on the flip.
So here's the theory, Rove decided the only way to get Cheney out of the way was to get him out of the way. I mean really, aren't you a little surprised Cheney is still there? Weren't they supposed to put in a "successor" by now? Now with the fighting from Cheney on Rove's re-working of the ol' Dick Morris strategy, Rove wants the guy out for good, and the guy won't leave. So Rove decides, instead of letting Scotter talk the fall, which was probably the end game (hey, they'll all get pardons anyway), he'll turn on Cheney and force the guy to be named as an unindicted coconspirator. A press conference later, they'll ask for Cheney's resignation. See ya later Dick. Now they've got two years to fix Iraq, get gas prices down to a reasonable level, and prep the new VP for the presidency.
Again, just a guess, but I really think Rove did it. Fitz's letter gives it away, I think. He's telling Rove, I'm offering no deal here, but if you've got a bigger fish for me, I'm interested.