Israel says it first bombed Iran to stop it from being able to produce nuclear weapons and the “existential threat” they would represent. But the conflict may in the long run serve the opposite purpose: illustrating to Tehran and other nuclear-aspirant nations that nuclear weapons are essential in shielding them against attack. Countries such as North Korea already pointed to Libya, whose leader Moammar Gadhafi gave up his nascent weapons program but was toppled anyway in 2011 after a NATO intervention. That’s one of the reasons Pyongyang has developed its own arsenal — which is believed to have San Francisco...