In international law, a “weapon of mass destruction” is a nuclear weapon, a biological weapon, or a “chemical” weapon (i.e., a poison). The inclusion of chemical weapons in the list has never made any sense; they’re exceptionally nasty weapons (though no more so than anti-personnel mines) but they don’t cause the sort of mass deaths that justify the label.
Still, that’s the way the term is used, and only pedants like me are likely to complain about it.
In post-9/11 federal law, however, the term “weapon of mass destruction” has been twisted even further out of shape. If some clown in Texas was doing on-line searches for directions on making IEDs and to find appropriate targets, and then went out and bought some of the chemicals, he belongs behind bars and I’m glad the FBI nailed him. But to call a roadside bomb a “weapon of mass destruction” – to link it with nuclear weapons – is simply insane.