His presentation to the UN security council was impressive in its delivery. He barraged the members with questions: "Who took the hard drives? Where did they go? What's being hidden? Why?" Yet he offered few answers and much speculation.
His voice was clear, his tone abrupt, his manner wavered between imploring and threatening. Time and again he assured his audience - an increasingly sceptical American public as much as his security council colleagues - that he was showing them "not assertions but facts" and "evidence not conjecture".
Falling back on his military credentials, at one point Powell conceded: "I am no expert on centrifuge tubes, but just as an old army trooper, I can tell you a couple of things."
The White House has been keen to play down any anticipation that Powell would produce a smoking gun. By the at halfway point of his address, the mood in the hall was weary; after all, Powell must have put forward his best evidence first.
By the time he had finished with a rousing call to action, if not war, people were looking at their watches.
It has been a dramatic shift in stance for the man who was dissuaded from running for president by his wife, Alma, who feared the threat of assassination.
In his autobiography, My American Journey, he wrote of the Vietnam war: "Many in my generation vowed that when our turn came to call the shots, we would not quietly acquiesce in half-hearted warfare for half-baked reasons that the American people could not understand."
It was Powell who argued before the Gulf war that sanctions should be allowed to bite before troops were sent in and argued against bombing in Bosnia because he believed it could not end the ethnic divisions that spurred the conflict. When his predecessor in the Clinton administration, Madeleine Albright, asked him "What's the point in having this superb military you're always talking about if we can't use it?" Powell said he "thought [he] would have an aneurysm".
But while it may have disappointed his diplomatic counterparts, Powell's speech may yet retain him some influence in the White House.
It was Powell who went to Bush on August 5 last year and persuaded him, against the advice of Bush's other key aides, to take the issue to the UN. He secured resolution 1441 in November after eight weeks of brinkmanship and against the wishes of hawks like Donald Rumsfeld and Dick Cheney.
Up until a month ago he appeared to be the only reasonable link between the White House and the world. At the beginning of January he implied that the inspections process still had longer to run: "The inspectors are really now starting to gain momentum."
The decisive moment in this evolution took place not, as many believe, last week when the chief weapons inspector delivered his critical report to the UN, but a week earlier following a security council meeting called to discuss terrorism.
The French, who were chairing the session, shifted the focus of the meeting on to Iraq, declaring the weapons inspectors needed more time.
Powell was furious. He described the French position as "unfortunate" in public, but in private he was angry.
A day after that, he said: "The question isn't how much longer do you need for inspections to work. Inspections will not work. It's the scepticism that we had all along to give Iraq one last chance for inspections to work."
There are those who believe that Powell has changed, only the perception of him has been corrected. The Powell doctrine has always been that the US should only use force as a last resort to protect America's vital interests, but that once force has been authorised it should be applied overwhelmingly and decisively.
"It is vexing that the argument is cast as hawks and doves - or in Nike language 'Just do it' against 'Just don't don't do it'." said one of his aides recently. "The Powell solution is 'Just do it right'."
But as his security council colleagues offered their sceptical responses yesterday it seemed that Powell had now adopted the Bush doctrine: "Just do it anyway."
