According to the orginal op-ed piece he did .. Wilson said he was told by the CIA ... aka his wife
http://foi.missouri.edu/terrorintelligence/whatididnt.html
In February 2002, I was informed by officials at the Central Intelligence Agency that Vice President Dick Cheney's office had questions about a particular intelligence report. While I never saw the report, I was told that it referred to a memorandum of agreement that documented the sale of uranium yellowcake — a form of lightly processed ore — by Niger to Iraq in the late 1990's. The agency officials asked if I would travel to Niger to check out the story so they could provide a response to the vice president's office.
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BTW ... Wilson apparently also said this
http://www.freerepublic.com/focus/f-news/993121/posts
"Neo-conservatives and religious conservatives have hijacked this administration, and I consider myself on a personal mission to destroy both." Those are the words of Ambassador Joseph Wilson, who will certainly be a household name for weeks to come
So he IS on a personal mission to destroy the administration, by his own words. And he won't hesitate to lie in order to succeed.