I don't quite agree. The ONLY way we will stop a terrorist attack from happening is to identify the threat before hand and then thwart it. Several million police on the street would not stop what happened today... well, that is, unless those several million are stopping every single person that walks down the street to inspect their bags, autos, etc. Counterterrorism the key to preventing these events. You can have all the police in the world on the street, but unless we revert to a police state, you will not stop them once they are sent out on their mission.