I don't think an Iranian nuke strike against Israel is very likely. They can't nuke Jerusalem because it it a Muslim holy site. Tel Aviv, which is not that far from Jerusalem, has a sizeable Muslim population down the road in Jaffa. The fallout from either strike would kill as many Arabs as Jews. There are few other major population centers that are either important enough or far away enough from Arab populations to make a strike viable.
Bear in mind that the Iranians are not Arabs, and most Arab countries are very nervous indeed about their upcoming capability, and you can see that their strike options in Eretz Israel are very limited indeed. A small, portable device is another matter, and would change the game completely, but these are very difficult to manufacture, and hopefully well beyond the capability of the Iranians at this point.
The real problem is that at the same time they are developing nuclear, they are also developing long-range strike capability, and already now have a 2000km multi-stage rocket. Bad news for the EU, very bad indeed.
This is why we need to take the gloves off, start supporting the dissenters and help facilitate regime change. This is probably our best and only chance to do it without something making a very loud bang.