Israel has had an arsenal of nuclear weapons since the late 1960s, and its current inventory is estimated at between 100 and 200 warheads. Some of these weapons will eventually be, or have already been, placed on Israel's missile-carrying submarines, making them virtually impervious to preemptive military attack. They are or soon will be Israel's invulnerable nuclear deterrent.
Yet, hardly a day goes by without some Israeli official, journalist or lobbyist expressing apocalyptic warnings about Iran's nuclear program. Iran, a state party to the Nuclear Nonproliferation Treaty (NPT), is in technical violation of some of its treaty obligations, but its program is still under international inspection by the International Atomic Energy Agency (IAEA). Israel never signed the NPT and thus is not under any international inspection regime.
The tacit assumption behind the apocalyptic pronouncements is that Iran will not only make nuclear weapons, but will use them to destroy Israel shortly thereafter. This amounts to assuming that Iran's leaders are insane. That is, Israel's deterrent notwithstanding, the Iranian clerics' hatred of Israel is so intense that in order to destroy it they would launch a nuclear attack that would kill not only Jews but also up to 1.5 million Muslims living in Israel, as well as triggering an Israeli nuclear counterattack. An Israeli nuclear counterattack, which Iran could not prevent, would turn back the clock on Iran's development for many decades and reduce its leaders to radioactive dust. There is no evidence to suggest that the ruling clerics are so disposed. Some have speculated that Iran might make nuclear weapons and transfer some of them to third parties, e.g. terrorist organizations, for use against Israel. But no country that provides nuclear weapons to a third party can be sure that the transfer will be perfectly secure from discovery or that the weapons will be used as intended. A nuclear attack on Israel using a weapon originating in Iran would undoubtedly be treated as if it came from Tehran, again resulting in Iran's utter destruction.