According to Michael Isikoff, the evidence is that Karl Rove was not the Valerie Plame leaker after all. Isikoff says it was Richard Armitage, then Colin Powell's no. 2 man at the State Department:
Armitage, a well-known gossip who loves to dish and receive juicy tidbits about Washington characters, apparently hadn't thought through the possible implications of telling Novak about Plame's identity. "I'm afraid I may be the guy that caused this whole thing," he later told Carl Ford Jr., State's intelligence chief. Ford says Armitage admitted to him that he had "slipped up" and told Novak more than he should have. . . .What a disappointment this must be to Joe Wilson, who wanted Rove marched out of the White House in handcuffs.
The disclosures about Armitage, gleaned from interviews with colleagues, friends and lawyers directly involved in the case, underscore one of the ironies of the Plame investigation: that the initial leak, seized on by administration critics as evidence of how far the White House was willing to go to smear an opponent, came from a man who had no apparent intention of harming anyone.