Some people believe that Iran has some power to inflict a war upon the US. This is not the case. Our Government is concerned about the proliferation of nuclear arms, and this causes friction between the US and Iran, as Iran seems intent on furthering its foray into nuclear enrichment, in search of nuclear weapons.
Naturally such weapons in the hands of radical regimes gives rise to the potential for terrorists to gain access to these devices for use against the US.
That being the case however, it does not improve the ability of Iran to wage war against the US. The assets simply aren't there. The army though largish, lacks the naval and air resources necessary to carry a war to the US. The logistics of such a war are beyond the capacity of Iran. It lacks the infrastructure, and the manufacturing base to supply an army on the march.
One nuclear weapon does not make a threat . The detonation of a nuclear device on US soil would be devastating, but in strictly military terms, insignificant. To inflict severe damage on the US fighting infrastructure would mean taking out, innumerable ICBM sites, submarines, ships, and aircraft.
This requires a level of intelligence gathering equal to that posed by the USSR in the cold war. Not only that but submarines to track our submarines, ships to engage our ships, and fleets of aircraft to fly against our air wing
Our allies are similarly armed, despite the isolationist rhetoric of some, no ally, no matter how tenuous their loyalty on issues during a peace, would tolerate the disruption of world markets that an attack on the US would mean, let alone allow a despotic regime access to the ultimate power.
All this aside the fundamental restrictions that applied during the cold war still apply. The reason the US and the USSR didn't devolve to thermonuclear conflict, despite high tension incidents such as the Cuban missile crisis is because of MAD, (mutually assured destruction). The only difference with Iran is that Iran can be assured of destruction, where as the US will undoubtedly prevail over attacks thermonuclear or not.
We should see the antagonistic stance of Iran to ourselves and its war like posturing in that light.