LOS ANGELES ― Revelations in former President George W. Bush’s recently published memoirs show that he declined an Israeli request to destroy Syria’s secret nuclear reactor in the spring of 2007. While the revelation may appear merely to be a historical footnote, more profoundly it raises new uncertainty about whether Israel now thinks that it can rely on the United States to apply military force to stop Iran’s nuclear program should diplomacy fail. The Syrian episode suggests that it cannot, which means that Israel may decide to go it alone once again, this time to eliminate Iran’s nuclear facilities.

If Israel did so, however, it would confront a conundrum. Unlike the attack on Syria’s nuclear plant, Israel’s conventional forces do not have the capacity to destroy Iran’s suspect installations. Portions of Iran’s nuclear program may be too heavily bunkered, dispersed or concealed. This raises the question of whether Israel’s repeated refrain that “all options are on the table” implies that even a nuclear strike is possible. Israel’s nuclear history provides no clear answer, but the future may force the issue.

Israel has never acknowledged having nuclear weapons, let alone the size and scope of its arsenal. Israeli policymakers refuse to talk about the subject. Israel’s parliament, the Knesset, never discusses the program or appropriates money for it. Military censors quash public discourse about it.

Yet American and other intelligence services and strategic-research institutes around the world all agree that Israel possesses nuclear weapons. They disagree about how many, with estimates ranging broadly, from 40 to more than 400 warheads.

Israel’s reluctance to rattle its nuclear saber, even in dire circumstances, adds to the mystery. In the Yom Kippur War, as Syrian forces threatened to break the country’s defensive lines, Israeli decision-makers recoiled even from threatening to use nuclear weapons.

While Israel keeps its bomb in the basement, it has a long history of stopping its adversaries. As Iraq moved to complete the Osirak reactor by the early 1980s, Israel applied diplomatic pressure and actions against foreign nuclear vendors, sabotaged atomic exports and assassinated Iraqi scientists, before finally settling on the June 1981 air strike on the plant. In the Syrian case, with one caveat, Israel decided to dispense with the preliminaries and simply destroy the reactor.

The caveat consists in a plea that Israel made to the U.S. According to Bush’s memoir, in the spring of 2007, Prime Minister Ehud Olmert made a blunt request of the U.S. president regarding Syria’s reactor: “George, I am asking you to bomb the facility.”

After consultation with his staff, Bush responded that, absent a plutonium extraction facility, U.S. intelligence could not confirm that the plant comprised a nuclear weapons program. “I told him (Olmert) I had decided on a diplomatic option backed by force” to stop Syria, Bush writes. An apprehensive Olmert responded, “I must be honest with you. Your strategy was very disturbing to me.”

Within months, Israel struck. One year later, it followed up by assassinating Mohammed Suleiman, the Syrian general in charge of resurrecting the nuclear enterprise.

Given its efforts to fend off an attack, Iran represents a far more difficult target for Israel than Iraq and Syria did. As a result, Israel ceded to the U.S. and others responsibility to move the Iranian regime from its current path.

Since 2002, the U.S. has applied a multi-pronged approach. It pressed the International Atomic Energy Agency for greater scrutiny. It got the U.N. Security Council to agree to impose increasingly onerous economic sanctions ― and roped allies into even stronger sanctions. It adulterated nuclear-related exports from European vendors to perform poorly during operation. It may have inserted computer worms into Iran’s atomic infrastructure.

The result of all these efforts has been to slow, but not halt, Iran’s nuclear progress. And, even as the U.S. and its allies attempt to restrain Iran, its regime continues to goad Israel, calling for its extinction and exporting military wares to its Lebanese and Gazan adversaries.

In May 2010, Israel responded with a new wrinkle. It leaked to the London Sunday Times that it had placed nuclear-armed submarines off Iran’s coast. In the months before and after, it continued to hold war games and practice air strikes on Iran. And it repeatedly uttered threats that “all” options are on the table. Iran remains unmoved.

Concerned that President Barack Obama will be less likely than Bush to use force to stop Iran, Israel must now contemplate its next steps should diplomacy continue to stall. One option would be to pursue a policy of “opacity plus”: a further lifting of the veil over its nuclear arsenal in order to caution Iran’s rulers about the potential consequences of their actions.

Another option would be to bring the country’s nuclear arsenal out of the basement altogether. Israel could then mimic other nuclear-armed states by flexing its capacity through announcement and transparent nuclear deployment on land and sea, thereby promoting deterrence.

But, for a country that has had little faith in deterrence when it comes to existential nuclear threats, relying on it now would mark a new, uncomfortable bet.

That leaves nuclear use as the final option. But nuclear attack carries its own heavy burden. Given Iran’s placement of strategic sites in or near population centers, the deaths of many thousands of people would forever tar Israel.

The only worse stain on Israel would be if survivors of an Iranian nuclear strike were to lament that, had their country acted proactively, “the third destruction of the Temple” ― the end of the Jewish state ― could have been avoided.

These sobering prospects should prompt all involved to seek a peaceful resolution. Time is growing short.

By Bennett Ramberg

Bennett Ramberg served in the Bureau of Politico-Military Affairs in the George H.W. Bush administration. He is the author of several books on international security. ― Ed.

(Project Syndicate)