No one is disputing that; the side issue is whether Wilson had already planned a business trip to Niger, and that the uranium investigation was an add-on at the suggestion of his wife.
I should clarify: no one is disputing that Wilson was dispatched to Niger in 2002 to investigate the Niger/Iraq uranium connection. The dispute (a minor one) is whether he was sent by the CIA or the White House. The answer is "both"; he was sent by the CIA in response to a request from the WH, but the WH did not know that he had been sent or what he found out in his investigation. And there is the side issue of whether his investigation was an add-on to a pre-planned business trip that just happened to coincide with the WH request for info about Niger.