During wartime, it is easier to encourage an enemy to attack you in a given place than it is to prevent an attack in a given place. Both can be difficult, but the first is much easier to accomplish and has been done countless times throughout history. The 2nd has been done many times as well. However, it usually was because an offensive was launched that forced the enemy to defend themselves in a different area. The problem with this strategy is that it requires having adequate resources to launch an effective attack. Counterattacks have been attempted many times without enough resources. The final result ended up being worse than allowing the opponent to attack in the first place.
Concerning the war in Iraq today, the U.S. is fighting the war with a peacetime army. Our enemy has nowhere near the resources that we posses, even with the U.S. on a peacetime footing. The war in Iraq and Afghanistan is preventing our enemy from attacking us effectively elsewhere.
The bad news is that our enemy has an ideology that is engrained in a huge population spread out over many countries. The war has the potential to become much larger even without the use of WMD. Or more likely, the war will last so long that the U.S. and its allies become tired of war and give up.
The good news is that the enemy ‘army’ would have to obtain much more overt help in order to force the U.S. to decide to mobilize. WMD is the most likely way that this would occur. Also, the U.S. can increase the size of it’s armed forces considerably, it if needed to. The use of WMD by our enemy would make this mandatory.