Iran would lose control of their airspace pretty quickly and we'd be able to drop bombs on whoever we want, but there's no quick way the United States could occupy and control the country in that time (at least, not without resorting to weapons and tactics that would cause massive loss of civilian life, and which most soldiers would I hope refuse to carry out).

Some of the logistical issues are explained here: https://www.electoral-vote.com/evp2020/Pres/Maps/Jan06.html

This is going to get very interesting in terms of internal US politics. The Democrats don't trust Trump, including in terms of his motives and judgment in dealing with Iran. They also, in general, oppose war. They're trying to use the War Powers Act to reign him in. But if they do so, and prevent a response to this latest attack, that could cost a number of them dearly in the next election - especially since Iran is not likely to stop at firing a few missiles at two US bases.

If casualties are non-zero, the President will be obliged to carry out his “52 targets” threat. This is probably the right move — don’t play tit-for-tat against a less powerful adversary, instead immediately escalate to a level they can’t possibly match.

Unfortunately Iran’s air defences are more potent than anyone the US has bombed recently, so we might be about to find out just how good US technology really is.

What happens next? I’m not sure. I can’t imagine the US committing to a ground invasion of Iran, but it should be possible with an air campaign to reduce Iran to the level of a 2000-era Iraq.

Edit: President Trump’s latest “all is well” tweet, and his intention to hold off on doing a briefing until tomorrow, seems to imply that US casualties were zero after all and that he’s chosen the “laugh it off” response, which is a great relief to me.