Why do some Americans use chemical weapons as "proof" Saddam had WMDs  to justify invasion when US sold Saddam those weapons?

And two American Presidents did NOTHING when Saddam put them to use against Iranian troops during the Iran-Iraq War, and then later used them against Kurdish civilians. The nonexistent WMDs were nothing more than an excuse for the invasion of Iraq, which would have been used as a jumping-off point for an eventual invasion of Iran - if the operation hadn't been so colossally bungled by the Bush II Administration.

The weapons inspections had already happened by the UN, and it was determined that he had destroyed all of his chemicals. But it wasn't enough for the US, the Bush admin already had set its mind up that it was going to invade, and so it did.

After signing the armistice agreement in 1991, the Iraqis continued to lie to ,and obstruct ,UN weapons inspectors ,and later they began to threaten them -- and in 1998, they left because it had become too unsafe and impossible to do their job. 

For the next few years , therefore, UN  weapons inspectors did not operate in  Iraq -- as was  required under the 1991 agreement. During this period ,however, Saddam H  not only continued to violated sanctions ,but continued to threaten the  surrounding countries by his actions.

By 2003 ,everyone, including the UN  agreed that something had to be done -- and that Hussein could not be trusted : the UN wanted weapons inspections to begin again --- but the US decided ,after the last experience of inspection , it had gone beyond that ,and the risk of not invading ,was too high .

At the time ,there were good reasons for invading Iraq -- whether we should have, is debatable still .

largely because of when Nancy Pelosi....for no other reason than to politically embarrass and discredit the President during wartime...pushed a Congressional resolution to condemn the Armenian Genocide...

...this so outraged our Turkish allies that they refused Coalition access to their bases, which prevented the planned establishment of a vital Western Front to seal the border between Iraq and Syria....

....it was through this unguarded border, of course, that billions of dollars worth of Saddam's assets flowed freely into Syria following the fall of Baghdad.... (it was also through this open border that many of the insurgents that killed American soldiers and terrorized civilians entered Iraq freely)....

...it is well known that those assets not only included much of the heavy arms that allowed ISIS to form into a legitimate military force, but also the mobile bio-weapon laboratories (and scientists that operated them) known to the UN...

in short, the reason only "old" WMDs were found after the war was because all of Saddam's chemical weapons and research was allowed to waltz into the hands of Assad in Syria (as evidenced by his later use of them)..... all because of political pettiness that has become the hallmark of Nancy Pelosi and her followers...

Becouse he still had them and they are WMDs.  Why use them as an example that he had? becouse they are definitive, can't be argued against.  Now the argument turns to they were/old or whatever. But that doesn't dismiss the fact that he was using them on the Kurd's and systematically trying to wipe them out.  The new stuff is still a bone of contention, they had new manufacturing equipment, new warheads built for chem weapons, all the ingredients, some found filled others empty at sites. Some claim they found new stuff while other still say he didn't.  Oh, what the US sold him, was supposedly destroyed, so he wasn't suppose to have that stuff either.