the US cannot win a war against Iran.
the USA cannot win and Iran has plenty of asymmetrical options ranging from riding out the attack to attacking CENTCOM targets all over the Middle-East.
the only boots on the ground to defeat Daesh have been, still are and will be, Iranian boots. That is a fact of life, sorry.
“we will make darn sure that you fail everywhere, in Iraq, in Syria, in Pakistan, and Yemen and everywhere else in the Middle-East”. And that won’t be an empty threat: the Iranians absolutely can deliver on it.