The Niger story became a CIA story when the credibility of Joe Wilson and the legitimacy of his mission needed to be explained.
Recall Wilson said he was on a mission from Dick Cheney's office? He was supposedly sent to Niger by the Vice President.
That was a lie and that lie led to the outing of his wife. Given the fact that Joe Wilson went public (no confidentiality agreement?) with lots of false information, his credibility needed to be exposed.
Joe Wilson is a partisan hack sent on a Niger mission by his CIA wife.
Now is that certifiable as a professionally hatched and executed CIA operation?
Obviously not.
It needed to be exposed. Note that Fitzgerald has not charged anyone with the crime of outing a CIA agent.
Wilson told two journalists, Pincus and Kristof, that he, Wilson, had debunked the forged Niger documents. The documents had recently been publically acknowledged to be fakes. Wilson made his statements to Pincus and Kristof at the same time that he had joined the Kerry campaign. The problem, however, is that Wilson had never seen the forged documents, his trip to Niger had nothing to do with them, and in any event Wilson's report never reached Cheney's eyes. So Joe got some splainin' to do there.