It has been proven. Hell Bush repeatedly suggested Iraq was involved in the 9-11 attacks and He refused to say otherwise till long after the invasion.
Nobody else was saying Iraq was close to building an atomic bomb other than the administration. He also used an Iraqi who was a convicted con-man and who The CIA and others told Bush couldn't be trusted to support His claims. The Administration also completely BSed about a terrorist training camp. They correctly stated it was in Iraq. What they didn't say was it was in the Kurdish no-fly zone where they were protected by American planes against Saddam. I'm not saying We deliberately protected them, but the camp WAS in American controlled space.
Most important, He used 9-11 to go after Iraq at the expense of finishing the job against Jihadist.
Bush was right about 9-11 changing the game, but just got the details completely wrong. What He should have seen was Iraq was a non-priority, they had no connections to the Sunni jihadist, in fact, the jihadist were Saddam's enemies for 40 years.