Yes USA can nuke Iran.

And North Korea, China and Russia could also nuke every ally to USA in Europa , the ME and Asia. Probably Australia too.

Leaving USA Russia China and North Korea standing.

Now who think that USA Alone would be able to defeat them?

How about a Russian submarine hidden in the Gulf of America suddenly nuking Washington?

I wonder if even Putin knows the exact whereabouts of all their Submarines.

That said, they did scrap most of them.