There is a widespread misperception that "there has not been another terrorist attack on American soil since 9/11." (For example CNN, 2004. New York Review of Books, 2006.) This, or a similar formulation, is repeated so often one could be forgiven for believing it.
The problem is, it is totally untrue.
There is, to my knowledge, only one time that the U.S. has been attacked by terrorists with weapons of mass destruction: the anthrax attacks on the U.S. Senate, prominently on Senators Daschle, and Leahy. It should be emphasized that the senate attacks used weaponized anthrax, constituting a weapon of mass destruction. This was in October of 2001.
You would think people would remember.
Why has this attack virtually vanished from public consciousness?
Perhaps because it was proven early on that the source of the attack was the U.S. government, specifically, "the original source [of the terrorist material] had to have been USAMRIID" (U.S. Army Medical Research Institute of Infectious Disease in Fort Detrick, Maryland.)
At a bare minimum USAMRIID failed to adequately police its own stockpiles of WMD, for which then, the U.S. government and the U.S. military are explicitly responsible.
A remarkable exercise in enforced amnesia.