Iran is not a pushover. In order to invade Iran US has to take on their unique Two set of Defense forces one is IRGC, which has its own Air force, Ground force, Navy, Quds forces and the other one is regular Islamic Republic of Iran Army, again which has all the Three components.
In an event of attack, Iran will just block the Persian Gulf, which will automatically cease the transit of crude oil from Gulf to the world hence a creating global chaos.
Iran army is not better than Iraq army
With
Slightly advanced Air defense and Artillery
There weaknesses is There Negligent Airforce.
But potent Ballastic arsenal.
It will hardly take US to acheive Air supremacy within few hours of Fight
After that it will be more fire and fury like Iraq
But casualties might go up in this on.ground
Unlike Iraq Iranians army is not corrupt
They will fight to death.
Ultimately Became bloody enough to US to reconsider currently seeing the Wokism is prevalent in there Civil Administration.
After Defeating Iran
Us Casualties can go up to 10000-15000 thousands
In coming weeks or months to sustain Country like Iran.