Israel's survival will depend on having a credible and reliable nuclear deterrent. Although it is possible for Israel to avoid a nuclear threat, Israel must remain alert for first-strike aggression. In such a scenario, Israel could counter the enemy using conventional weapons before resorting to nuclear counterretaliation.
This is a real dilemma for Israel. A strategic calculation of the benefits and costs of a strike would need to be made. Jerusalem's evaluation of the enemy's intentions, and the essential damage-limitation would all be factors in this calculation. If the enemy's intentions are clear, then a nuclear first strike might be justified. But, if Jerusalem's judgments seem ambiguous, the first strike might not prove to be the most wisest.
You can strike preemptively without a lot of risk, provided you have the right strategic circumstances. A defensive first strike is legal, as long as it is justified under international law. A strike by the enemy to disrupt Israel's military order of battle would be illegal. The enemy could impede the strike by launching a preemptive strike, or launch a chemical or biological response.
Israel could choose to preemptively strike Iran if the enemy responds. This would decide Israel's next move. The preemption process would influence the enemy's response by influencing both strategic and jurisprudential assessments. Depending on the severity and extent of the provocations, the enemy's reaction would be judged rational or irrational. If the enemy's answer is irrational it can be deemed rational and Israel could choose to strike first.
Israel might then be tempted by Iran to strike first with conventional weapons, before resorting to nuclear retaliation. In such a situation, decision-makers would decide whether Iran's nuke weapon arsenal would be sufficient to deter Israel and whether Iran's counter-retaliation could prevent Israel from attacking. If the enemy responds only to conventional retaliation the nuclear counter-retaliation is not possible.
If Israel decides to preemptively attack Iran, it must ensure that its strategy and tactics are legal, and that the decision is in line with authoritative expectations. It is also prudent to consider Iran's mutual judgments. If Israel chooses to preemptively attack and retaliate against Iran with conventional weapons, then it could be a false pretext for aggression.
The nature of Israel’s nuclear strategy would also impact Jerusalem's strategic choices. Israel with nuclear weapons would be less likely not to threaten nuclear retaliation for minor territorial infractions. Israel may not have nuclear weapons and could therefore be less likely to threaten nukes for terrorist incursions.
Jerusalem would also be able to use nuclear weapons, and would likely have a nuclear arsenal, if the enemy had a nuclear weapon arsenal. The Israeli decision-makers would determine whether Iran's atomic arsenal could deter Israel from attacking, and if Iran's nuclear weapons could deter Israel from attacking, then the decision to preemptively attack would be legal. If Iran's nuclear arsenal failed to deter Israel, the decision would be illegal.