He may have been suggested by his wife, as the wingers claim and he somewhat cagily denies (usually by citing news reports, as though the subject is someone else). The CIA's motive (not Tenet's, but the analysts in charge of nonproliferation who sent Wilson) may have been to add substance to the skepticism against the Niger documents claiming Iraq was trying to buy 550 metric tons of yellowcake.
Wilson, oddly enough, admits (in his
NY Times editorial of July 6, 2003) that he never saw those documents. He also says in that editorial that his role in refuting the Niger story was "small."
Rereading the Wilson documents is rather rewarding. It explains why Bob Somerby of the Daily Howler is so hard on Wilson. He can be maddeningly vague--lots of passive-voice constructions in which the actor in the sentence is not clear. It's difficult to get a handle on why Wilson was sent at all. The documents had already been debunked by textual analysis, and the embassy and a military analyst on the ground were already looking into whether or not anyone in the Nigerian government had contacts with Iraqis. The ambassador to Niger asked Wilson not to talk to anyone in the current government, so Wilson only talked to former ministers. He never wrote a report, he merely gave an oral briefing to the ambassador and his contacts back at CIA. Oddly enough, his analysis was graded a middling "good" because he added one little piece: Evidently an Iraqi delegation did show up in Niger, but the Nigerians said they didn't talk about yellowcake because it was understood to be off limits. (So what did they talk about? The report doesn't say.)
In any case, Wilson's piece corroborated the rest of the analysis suggesting that Iraq got nothing from Niger in 1999, certainly, and nothing in Niger supported the Bushists' "fear" (or hope) that Iraq was immanently rebuilding its nuclear weapons program in 2002-2003. Which leads me to conclude that the point of Wilson's editorial (that the Bushists were knowingly exaggerating the threat to justify the rush to war) was essentially sound.
The question of who sent Wilson, in short, is irrelevant to the main question: did the Bushists "fix the facts and intelligence around the policy" so they could throw an illegal war? And did they try to smear Wilson and his wife to throw the media off the scent leading to the real meat of the issue?
Duh!