We cannot financially afford to get involved. We don't have any money to go to war with Iran.
Also, war with Iran would not just be war with Iran, but would probably end up leading alliances being formed between Russia and Iran (they border each other), and it would also piss off about a billion other Muslims in the middle east who are obviously itching for an excuse to raid all our bases across the middle easy because they themselves are exhausted from our presence and heavy-hand there.
And why would Iran ever nuke Israel? Israel has hundreds more nukes than they will have in any near foreseeable future... do you think they are that dumb to nuke someone with more nukes than them? Kind of like bringing a knife to a gun fight...
At the end of the day, we're already broke, our military is exhausted, we are all restless from war, and we want to go and instigate a war which could very easily lead to a WWIII scenario with a billion people pissed at us. Yea, OK.
Regardless of who is evil and not evil - I think we're asking all the wrong questions. We all know that this is more or less about the oil and the dollar. That's the only thing that makes any sense right now of why the US even cares about this.