Mr. Obama, like his predecessors, pretends that he doesn’t know anything about them. This taboo impedes discussions within Washington and internationally. It has kept America from pressing Egypt and Syria to ratify the chemical and biological weapons conventions. Doing so would have brought immediate objections about American acceptance of Israel’s nuclear weapons.

What sustains this pretense is the myth that America is locked into covering up Israeli nuclear bombs because of a 1969 agreement between President Richard M. Nixon and Israel’s prime minister, Golda Meir. For Mr. Nixon, it was mainly about gaining Israeli support in the cold war. He and Mrs. Meir understood the need to discourage the Soviets from providing their Arab allies with nuclear weapons. A declared Israeli nuclear arsenal would have led to pressure for Moscow to do so. But such cold war reasons for America to stay mum evaporated decades ago. Everyone knows the Israelis have nuclear bombs. Today, the main effect of the ambiguity is to prevent serious regional arms-control negotiations.

All other countries in the region are members of the nonproliferation treaty, but there are still unresolved issues. Syria was caught building an illicit nuclear reactor in 2007, which Israel swiftly bombed. Mr. Assad still has not allowed international inspectors to fully investigate that obliterated reactor site. And Syria’s ally Iran is suspected of trying to assemble its own weapons program to challenge Israel’s nuclear monopoly. Indeed, many analysts believed that Mr. Obama’s decision to issue a “red line” barring the use of chemical weapons in Syria was in fact driven by the perceived need to demonstrate that he was prepared to use force against Iran if it moved further toward nuclear weapons.