Actually, Cheney and his staff were put on Cipro on September 11 (
see, for example, Low on the Food Chain). Either Saddam made a direct threat, through channels, or the whole scenario had been wargamed beforehand. The latter seems quite likely. After all, the way events have unfolded -- Saddam sponsors massive terror attack in revenge for Gulf War
et seq, backed up with the threat of anthrax to deter US retaliation -- is simply the unfolding of a rather predictable scenario, given the personalities and capabilities of the players involved.
Good point. It is also possible that the Florida anthrax was from Atta's group and the weaponized stuff from a scientist.