American troops have been dragging around gas masks, and other chemical war protective equipment, for over 80 years. That's a fact. For all that time, a lot of this equipment didn't work. That's also a fact, but one only the troops, and not all of them, know about. Gas masks, the most common protective gear, only work if they fit well and their filters are still fresh. The only way to test the masks is to have the troops put them on and have them stand in a cloud of tear gas for a few minutes. For years, soldiers went through this exercise in basic training. Those masks were kept in good working order, as any failures were quickly noted when troops got a whiff of tear gas. But once with their units, the gas mask got nothing beyond a visual examination. Moreover, combat troops rarely kept their gas masks when they went into combat. The damn thing was extra weight and there were more immediate needs to be lugged around, like ammo and food. For over sixty years, you could always tell if fresh American troops had passed through a battlefield, for it was littered with discarded, fairly new, gas masks. 

In the 1970s, the Pentagon became aware that the Soviet Union had decided to "go chemical" in any future war and were stockpiling thousands of tons of chemical weapons. So new chemical protective gear was designed and produced. But in the combat units, it was still impossible to get commanders or troops to devote sufficient time to taking care of their chemical protective gear. So the matter was ignored. To a large extent, it still is. Every year or so, someone, somehow, tests chemical protective gear and finds it wanting. On the bright side, if chemical weapons are used against American troops, some of the protective equipment will work. There will be higher casualties than expected, but it won't be a catastrophe. But one reason for warning any potential users of massive retribution if they use chemical weapons is because the generals were once commanders of combat units. They know the state of the chemical protective gear, and they know it probably hasn't changed no matter how many orders they have issued to sort things out.

Just another reason to fear chemical weapons.