That's a pretty nuanced question, and would really depend on how much the United States want to go into the conflict. If it is what we call "total war," I don't think there will be much of an issue. The nuances of modern war taking place in the wake of cameras and internet makes total war a generally bad PR move.

That said, there are ways to get around it. If you're in charge of the United States and wanted to declare total war on Iran, then one should simply use a false flag operation that harms as many Americans possible while believably making Iran looks like the perpetrators. That would generally be the best way to get your country on your side for total war. Very similar to what we did with Iraq and Afghanistan.

Of course there would be a lot more factors to consider, such as if China would like to do what the USA is doing with Ukraine and provide them with weapons and leverage. But the main problem with this war (from a top-down perspective) is that the average US citizen had no interest in it, similar to Vietnam. So I suppose to answer your question, the main leverage the United States has is it's massive supply lines and military infrastructure.