The US is not configured to deploy everything it has in one theatre. This is not a realistic scenario. You've clearly have never dealt with real world logistics in your life, if you think that's even remotely possible. And even if this fantastical feat of creating supply chains to the region for sustained war was possible, there's very little chance of the US overrunning anything. You only have to look at a map to realize that Iran is a very mountainous country that would be a nightmare to fight in.
Finally, the US army is configured for legacy 20th century warfare. NATO as a whole is entirely unprepared for what modern war looks like. This is part of the reason the US is already getting its ass kicked by Iran, not being able to establish air dominance which is the core part of NATO fighting doctrine.
here's how NATO fared in recent exercises with Ukrainian veterans https://www.youtube.com/watch?v=iAg4qBaFvjI
and here's how well US army is prepared to deal with drones https://www.youtube.com/watch?v=ETeA07YjnSM