Bush: Don't Give Peace a Chance

The Downing Street Memo, notes of a July 23, 2002 meeting of Tony Blair and his top advisors, pretty well makes it clear that, 8 months before the actual invasion, Bush was looking for reasons to go after Saddam Hussein:

C [Director of SIS (aka MI6) Sir Richard Dearlove] reported on his recent talks in Washington. There was a perceptible shift in attitude. Military action was now seen as inevitable. Bush wanted to remove Saddam, through military action, justified by the conjunction of terrorism and WMD. But the intelligence and facts were being fixed around the policy.
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No decisions had been taken, but he [British Defence Secretary Geoff Hoon] thought the most likely timing in US minds for military action to begin was January, with the timeline beginning 30 days before the US Congressional elections.
The Foreign Secretary said he would discuss this with Colin Powell this week. It seemed clear that Bush had made up his mind to take military action, even if the timing was not yet decided. But the case was thin. Saddam was not threatening his neighbours, and his WMD capability was less than that of Libya, North Korea or Iran. We should work up a plan for an ultimatum to Saddam to allow back in the UN weapons inspectors. This would also help with the legal justification for the use of force.
The [British] Attorney-General said that the desire for regime change was not a legal base for military action.