If they ever had WMDs, they'd have used them to defend themselves against our invasion. They didn't. QED, there were no WMDs.
That proves nothing... the US maintains a military policy of "You use WMDs on us, we will use MORE OF THEM on you."
Germany in WW2 had WMDs, specifically chemical weapons. They absolutely had them and we know because that is in part how they managed to industrialize genocide by using said chemical agents to speed up the killing process.
Yet they NEVER used them on the Allied forces even when they were losing the war. Why? Because Hilter, and the German command, knew that the US still had MASSIVE stockpiles of Mustard Gas and other such WMDs and would use them. Likewise the Japanese had many chemical weapons (and biological) as mentioned above. They deployed them against China, but not against the US (OK,
technically they did try and use a biological weapon against the US, but it was such a weird niche and longshot effort that nobody knew they'd tried it until something like the 1990s because of how unsuccessful it was), but chemical weapons and the like? Zilche despite some of the worst fighting because, again, they knew the US would respond in kind... and escalate (and, considering we then dropped nukes on them...).
Look, the US has lost a lot of it's backbone since WW2. I don't think many in the US would have the stomach for using WMDs. However, nations don't gamble that the US has lost that much backbone when it comes to the WMD game. If you gamble on it and win your country is still facing down a military power with no present peer and your WMDs probably only slowed it down a little bit. If you gamble on it and
lose? Going forward your country would be spoken of in
past tense. When your options are "fast military defeat", vs. "military defeat" or "annihilation", you generally don't go with the one that has a chance of "annihilation".