I don't think the US can win simply because we'd be going in without galvanizing our base.
Afghanistan happened because everyone was furious over 9/11. Iran is happening for no reason at all. I'm not in the army but I can't imagine being all that motivated when it feels like I'm risking my life for nothing.
The lack of political capital also means the US population is much less willing as a whole to swallow losses. Imagine if gas jumps to $6/gal. Who the fuck wants to eat those kinds of costs?