MSNBC

According to the report linked above, a Pentagon official (as opposed to some "top Republican") stated as follows:

At the Pentagon, an official who monitors developments in Iraq said U.S.-led coalition troops had searched Al-Qaqaa in the immediate aftermath of the March 2003 invasion and confirmed that the explosives, which had been under IAEA seal since 1991, were intact. The site was not secured by U.S. forces, the official said, speaking on condition of anonymity.
In other words, this cache of explosives did not vanish before the troops arrived. The International Atomic Energy Agency had secured these explosives before the war. They were still there when U.S. forces arrived. The U.S. forces didn't bother to secure them, and so they were stolen.

And why is this a big deal? Because we're talking about 360 TONS of explosives, one POUND of which is enough to blow an airliner out of the sky. We're talking about explosives that are very likely being used right now to kill and maim our soldiers.

But these are conventional weapons, not WMDs, so this administration wasn't interested in them. Just another example of the shortsighted arrogance that has been characteristic of Bush & Co.