Looked up some dates:
Iraq invaded Kuwait August '90.
America and other allies took first definite action in January '91.
Last action in March '91.
My personal recollection is that though Bush's approval rating was high after the swift conclusion of the Gulf War, it wasn't enough to offset public discontent over economic woes. When taxes went up Bush was perceived as having lied with the famous "Read my lips; no new taxes" speech and that hurt him far more than the Gulf War helped him. Again, just a personal recollection of how things shook out.
So there's no guarantee that if Dubya prosecuted a swift and decisive war with Iraq right now, that public opinion would see him safely through the next year's election. From this amateur's perspective a war might actually do him more good if it occured closer to the election. But there could be any number of reasons, the "winter window" I mentioned not even being one of the best. Like maybe he's leery of having Congress rescind the power to attack Iraq (not bloody likely, but a possibility) and wants to get it done now, while he has the power. Or maybe he's trying to please his corporate masters so they'll fork over big for the campaign. Quien sabe?