I'm about done with this thread, but I did want to point out some awkward realities of the period.
Iran was almost the US last Cold War strategic linchpin in the region. Geopolitically, there weren't a lot of good options.
Iran was adjacent to the Soviet Union. If you actually pushed Iran into a corner, declared war, etc., that corner would be the Soviet corner. The Soviets would have to turn to someone for new military supplies, weapons, ammunition, etc., and that would have been the Soviet Union. Iran was equipped with a vast amount of American military gear, but there's no question but that the Soviets could have met any level of demand for interim parts, or facilitated a changeover. It would have been a huge windfall for the Soviets, an infinite pipeline of weapons for the Iranians, and worst of all extended Soviet presence and influence all the way to the Persian Gulf. Suddenly, it could be the Soviet Union sitting on the Strait of Hormuz.
Of the other countries in the region, only Turkey could be termed a reliable American ally.
Iraq was already in the Soviet camp. The Soviets would try to keep it, and might well be in a position to succeed. Even if it couldn't, the Soviets had already demonstrated their willingness and ability to successfully switch horses in the Somalia/Ethiopia situation.
Pakistan was a nominal US Ally, but uninvolved in the region, unreliable, and had fought and lost three wars with India, their Bete noir.
Saudi Arabia and the Persian Gulf states were riding high in OPEC. And they were pissed off with the West over the whole Israel thing - the wounds were pretty fresh and the whole Egypt/Israeli peace thing was pretty new and fragile.
You could have seen varying degrees of Soviet influence throughout the region, which would have magnified Soviet influence in Europe and Japan, both of which were dependent on Persian Gulf oil.
So yeah, declare war, commit to some pissy regional spat, and fuck your entire geopolitical situation. At best, a worldwide body blow, at worst.... WWIII.
There's also the question of what we were going to declare war with? We had no local assets or bases in the region, and it wasn't likely we were going to acquire them overnight. This would mean monstrous logistical challenges in terms of force projection.
There was no question of occupying or invading a country ten times the size of South Vietnam, or Two and a Half times the size of Texas. A country with a population three or four times that of Vietnam. We simply did not have the army, and they simply were not up to the job.
Conceivably, we could have made war on Iran.... America at this time is still the Richest and Most Powerful country in the world - at worst we could just throw bullets made of money at them. But a war was going to be incredibly expensive, incredibly risky, and the stakes we committed ourselves to would be insane.