Who cares anymore if we find them or not? The whole world has seen the way that Saddam's regime paraded and abused our POWs (just wait until the full story of PFC Lynch comes out), the way they killed their own civilians, the way they hid massive amounts of weapons in schools and hospitals, the way they hided in mosques, the list goes on. Also, it is apparent that the Iraqi people have been brutalized by this regime, we have only seen the tip of the iceberg of those horror stories. When the full story of Saddam's regime comes out, people who criticize us for liberating Iraq are going to look like the nutcases who still defend Adolph Hitler and say that the Holocaust never happened.
Besides, we dropped something like 15,000 bombs in Iraq already. We can always just say that our bombs must have destroyed the stocks of WMDs (as they probably did).
Domesticly,Dubya is going to have a massive[and I fear fatal] pr problem and Republicans in general will pay dearly if there are no weapons found. Internationally, the chortling from France will be unbearable and humiliating. As a "superpower" we will be wounded for years after such a debacle.
No amount of spin about freeing the Iraqi people will fix that.