"If he knows he's going down, Hussein has no reason to hold anything back," warns Richard Betts, the Leo A. Shifrin Professor of War and Peace Studies at New York's Columbia University.
Mr. Betts, a military-affairs and terrorism analyst, believes there is a "one in five" chance that Iraq may attempt to attack the United States directly.
Mr. Bush warned this week that Baghdad could launch an unmanned drone from a ship to spray anthrax hundreds of kilometres inland. Far easier, and no less effective, would be an envelope of spores dumped into the subway systems of New York and Washington that could cause tens of thousands of casualties.
The longer the war lasts, the more casualties, the greater the risks. Images of besieged Baghdadis dying in the streets or hordes of fleeing refugees will be beamed to a worldwide audience, enflaming passions on Arab streets.
"To avoid a cascade of unintended consequences, Bush must use the firepower he is assembling in the gulf as a terrible swift sword that beheads Saddam in a single stroke," Strobe Talbott, former undersecretary of state in the Clinton administration, wrote in Yale Global on-line. Even if fanatic Iraqi troops were to spray anthrax or nerve gases across the path of invading U.S. troops -- causing hundreds of thousands of Iraqi civilian casualties -- "a lot of Arabs are going to believe we did it," Mr. Betts said.
The spectre of the Iraqi ruler gassing his own people, torching oil fields to create mayhem, and lashing out with missiles against Israel all to ignite anti-U.S. fury across the Arab world are not just worst-case scenarios. Mr. Hussein's track record of desperation in defeat includes all three.
It could be worse this time.
In 1991, Iraq refrained from loosing chemical weapons against the U.S.-led coalition troops and didn't tip the scores of Scuds it fired into Saudi Arabia and Israel with nerve gas, deterred by Washington's blunt warning that using weapons of mass destruction would bring a nuclear response.
But in 1991, the U.S.-led coalition wasn't headed for Baghdad to oust the dictator.
This time, Mr. Hussein knows the U.S. military objective is to unseat him, not just push the Iraqi army out of Kuwait.
Although there is no evidence that Iraq has mastered putting chemical or biological warheads on medium-range Scud missiles, Mr. Betts and other analysts believe he will launch them at Israel if he can.
While Israel might hold back if it suffered a handful of casualties as it did from conventionally tipped Scuds in 1991, hundreds of casualties might provoke an Israeli nuclear response; just the trigger for a war engulfing the region that might suit the Iraqi leader in extremis. Mr. Hussein seems unlikely to repeat his mistakes of 1991, when he left his army exposed in the desert to be pulverized by coalition bombing and then cut off and destroyed by encircling U.S. tanks. Already, there are reports that his best units are being deployed in and around Baghdad and Mr. Hussein's hometown of Tikrit, their tanks dispersed in mosques and near schools safe from U.S. warplanes and ready for a last stand.
Baghdad has more than four million people and even a few determined defenders could re-create the ghosts of Somalia or Vietnam for senior American commanders. "What worries me most is if we end up getting into protracted combat in cities, in downtown Baghdad," said retired U.S. general Norman Schwarzkopf.