They can't go toe-to-toe with us, but it won't be the cakewalk everyone pretends it will be. Along with their main forces, they have millions of Basij, loyal Shiite militias all over Iraq, along with Hezbollah forces in Syria and Lebanon. On top of that, our relations with Turkey are strained. They have already said they'd defy oil sanctions. Who knows what Erdogan would do. It'd get really ugly really fast.
There would likely be domestic terror, as well. In 2011, they had plotted to kill the Saudi ambassador at a restaurant, then bomb the Saudi and Israeli embassies. More than likely, they have people here with orders to carry out various tasks, should a conflict occur.
