Who is Woodward's "Mr. X?"

We're guessing it's also Novakula's first source. Downie tells the Times that if another Post reporter ID's him, they'll publish the name. The Journal seems to rule out a bunch of candidates, including Smirk and Snarl and Card and Bartlett and Condi and Rove and Libby and Hadley and Feith and Tenet and McLaughlin and Powell and Bolton and Ford and Grossman -- but not Rummy or Wolfie (he denied it, as did Karen and Ari and Andy to the Times) or Armitage or Wilkerson -- unless someone's lying, which can't be ruled out. We're running out of senior administration officials here. We think we'll find out sooner rather than later.
UPDATE: Or maybe not:

WASHINGTON (Reuters) - In a sign he may seek new or revised charges in the CIA leak case, special counsel Patrick Fitzgerald said on Friday his investigation would be going back before a grand jury.