Hopefully the thought of mutual assured destruction (MAD) will prevent a nuclear war, or even a war with Iran full stop.
This threat (MAD) prevented the former USSR and the USA from starting a nuclear war, even though they were on the brink of it a couple of times. India and Pakistan have also restrained themselves for this very reason even though they have been in conflict for a long time.
If Iran were to attack Israel, surely they would know that the response from the USA would be annihilation.
Unfortunately the innocent people in all of this are the citizens of Iran. They have a nutcase leader that they didn't even vote for taking them down a very dangerous path.
Fingers crossed cool heads will prevail, or alternatively Iranians once again organise a revolution and cut the problem off at the head (pardon the pun).