From The New York Times article Why Dick Cheney Cracked Up (reposted on TruthOut.org):
In terms of the big issues, the question of who first leaked Ms. Wilson's identity (whether Mr. Libby, Richard Armitage, Ari Fleischer or Karl Rove) to which journalist (whether Mr. Woodward, Mr. Novak, Judith Miller or Matt Cooper) has always been a red herring. It's entirely possible that the White House has always been telling the truth when it says that no one intended to unmask a secret agent.
But if the administration is telling the truth on these narrow questions and had little to hide about the Wilson trip per se, its wild overreaction to the episode was an incriminating sign it was hiding something else. According to testimony in the Libby case, the White House went berserk when Mr. Wilson published his Op-Ed article in The Times in July 2003 about what he didn't find in Africa. Top officials gossiped incessantly about both Wilsons to anyone who would listen, Mr. Cheney and Mr. Libby conferred about them several times a day, and finally Mr. Libby, known as an exceptionally discreet White House courtier, became so sloppy that his alleged lying [in grand jury testimony] landed him with five felony counts.
The explanation for the hysteria has long been obvious. The White House was terrified about being found guilty of a far greater crime than outing a C.I.A. officer: lying to the nation to hype its case for war. When Mr. Wilson, an obscure retired diplomat, touched that raw nerve, all the president's men panicked because they knew Mr. Wilson's modest finding in Africa was the tip of a far larger iceberg. They knew that there was still far more damning evidence of the administration's W.M.D. lies lurking in the bowels of the bureaucracy