Soon, if it has already decided against preemption, Israel will need to select appropriately refined and workable options for dealing with two separate but interpenetrating levels of danger. Should Iranian leaders be judged to meet the usual tests of rationality in world politics, Israel will then have to focus upon reducing its longstanding nuclear ambiguity, or, on taking its bomb out of the "basement." It will also need to operationalize an adequate retaliatory force that is recognizably hardened, multiplied, and dispersed.
This second-strike nuclear force should be made visibly ready to inflict "assured destruction" against certain precisely-identifiable enemy cities. In military parlance, Israel will need to convince Iran that its strategic targeting doctrine is "countervalue," not "counterforce." It may also have to communicate to Iran certain partial and very general information about the sea-basing of selected Israeli second-strike forces.
Should Israel's leaders conclude that they may have to deter an authentically irrational enemy leadership in Tehran, they will also have to consider the possible strategic benefits of appearing to their Iranian foes as a "mad dog." More technically and philosophically, this consideration would express a strategy of pretended irrationality. Together with any such planning, Jerusalem and Tel-Aviv, both civilian leadership and military, will need to determine: (1) what, exactly, is valued most highly by Israel's Iranian enemies; (2) how, exactly, should Israel then leverage fully credible threats against these core enemy preferences.
Under international law, war and genocide need not be mutually exclusive. In the best of all possible worlds, Israel might still be able to stop a nuclear Iran with cost-effective and lawful preemptions; that is, with defensive first strikes that are directed against an openly-belligerent and lawless Iran. Fully permissible, as long as they were judged to conform to the Law of Armed Conflict, such discriminating and proportionate strikes, conspicuously limited by peremptory rules of "military necessity," could still represent authentically life-saving expressions of anticipatory self-defense.
But this is not yet the best of all possible worlds, and Israel's Prime Minister Netanyahu will almost certainly have to deal with a nuclear Iran as a fait accompli. With this in mind, all early critical estimations of Iranian rationality will need to be correlated with appropriate Israeli strategies of defense and deterrence. Even in a "worst case" scenario, one in which Israeli military intelligence (Aman) would determine a compelling risk of enemy irrationality, a thoughtful dissuasion plan to protect against Iranian nuclear weapons could still be promising.
This binary plan would seek to comprehensively deter any Iranian resort to nuclear weapons, and, simultaneously, to intercept any incoming weapons that might still be fired if deterrence should fail. While the warning is now often repeated again and again that Shiite eschatology in Iran could welcome a cleansing or apocalyptic war with "infidel" foes, such a purely abstract doctrine of End Times is actually apt to yield to more pragmatic calculations. In the end, high-sounding religious doctrines of Final Battle that were concocted in Tehran, will likely be trumped by far more narrowly mundane judgments of personal and geo-strategic advantage.