Iran's not playing on the 'mighty' playing field - that's the one we're playing on. They're playing on the 'human strategy of the crazies' field.
So your example above about suitcase nukes is important.
Let's say three 'suitcase' nukes go off - two in Israel and one in Tampa. Iranian officials are in a meeting with this President or the next one or the one after that... and the Iranian official turns to the President and says, "there's nothing left of Israel so there's nothing to 'fight over' - AND we have 5 more suitcase nukes in American cities ready to explode - including one in DC if you decide to retaliate. So, Mr. President what's your decision: Peace or millions more dead Americans?
Now, just for the fun of it - let's play on the extreme strategy field for a while and come up with a solution to the above scenario...
You are missing several factors. Just 1:
If Iran detonates two suitcase nukes in Israel, that will not significantly affect Israel’s capacity to nuke Iran - and Israel WILL then turn Iran into a glass sheet. I doubt Iran will even have time to announce their follow up “threat”.
The Iranian mullahs are “crazy”, but, most of the present leadership is not THAT crazy.
Substitute a nuked up SA for Israel, and the suitcase bomb strategy is even weaker. (And in the shorter term you are more likely focusing on, SA will just turn to the Paks.)
I’m not saying the suitcase bomb strategy is impossible, but I think it is far less likely than the inevitable results of a nuclear arms race in the ME.
Either way, we CANNOT allow Iran to get nukes, and that’s what this is all about.