Every three weeks or so, within a few hours of one Israeli leader or another making a statement about the threat of Iran's nuclear program, my phone starts lighting up. It's never the press, which has become inured to Israel's periodic warnings. Rather, it is nervous hedge fund managers and securities research analysts calling to find out if this is "it." Are the Israelis on the verge of attacking Iran's nuclear facilities? No doubt, should Israel launch airstrikes against the Bushehr reactor or the uranium enrichment facilities at Natanz, it would be a market-shaking event. "No," I assure the financial whiz kids on the other end of the line, explaining that "if Israel's leaders were going to strike, they would not be broadcasting it to the world." The phone will then go quiet for a few weeks until the next time Shimon Peres, Ehud Barak, Benjamin Netanyahu, an Israeli security consultant, or my cousin Ari warns that time is running out.

Yet, despite my best efforts to walk a few financial analysts off the ledge, a mystery remains: Why haven't the Israelis attacked Iran's nuclear facilities? After all, Israel is a country born of the blood-soaked history of Jews in Europe, and Iran's leaders seem to be promising a new Holocaust. One would think there is already justification enough to dispatch every plane in Israel's arsenal to attack Iran's nuclear infrastructure. Also, between 2001 and 2009, the Israelis enjoyed the support of what was indisputably the most pro-Israel American administration in history. President George W. Bush and his advisors helped enable the Lebanon war in 2006 in the hopes that the vaunted Israel Defense Forces (IDF) would deal Hezbollah a fatal blow, so why not take out the Iranian mother ship, which poses a far greater threat to Israeli and U.S. interests in the region than Hezbollah's guerrilla army?

The standard wonk answers to these questions are that Israel does not have the capacity to fly its F-15s to Iran and back, that there is uncertainty about the actual targets, that there is too much risk of an inadvertent clash with possibly Turkish or even American aircrews, and that the Israelis are in fact giving diplomacy a chance -- despite all evidence that Jerusalem is profoundly skeptical that anything Washington can offer Tehran will bring its nuclear ambitions to heel.

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The New York Times caused quite a stir in January when it reported that Israel's defense and political leaders repeatedly sought permission from the Bush administration "to go," but were denied U.S. approval. Still, why didn't Israel attack anyway? Would Bush have ordered U.S forces to shoot down Israeli F-15s as they streaked across the Baghdad sky on their way to Iran? Unlikely. Confronted with a fait accompli, the Bush White House -- even if it were so inclined -- would not have been in a position to condemn an Israeli attack. Given his axis of evil and "with us or against us" rhetoric, it would have been decidedly awkward for Bush to come down on the Israelis for striking a blow against Iran. Moreover, the Israelis set a precedent for not informing the United States of dramatic military operations when on June 7, 1981, the Sunday morning routines of Reagan administration officials were disrupted with reports of the smoldering ruins of what was Iraq's Osirak nuclear facility.

Given Israel's perception of an acute Iranian threat and its demonstrated ability to act alone, there must be some other factor holding the Israelis back. Most likely, that factor is politics, and more specifically, the importance that close relations with Washington has on the domestic political calculations of Israeli leaders. Unlike in 1981, when the United States had barely a toehold in the Middle East, Washington occupies two countries in or adjacent to the region, maintains military facilities throughout the Persian Gulf, and relies on Arab governments for logistical support. In the event of an Israeli attack, Washington would surely be accused of colluding with Jerusalem, severely damaging the United States' position in the region while provoking a ferocious Iranian response in Iraq, Afghanistan, Gaza, and southern Lebanon. The resulting breach between Israel and the United States would be unprecedented, creating a crisis far more serious than President Dwight Eisenhower's demand that Israel stand down after its invasion of Sinai in 1956 and Gerald Ford's "reassessment" of 1975 (which suspended all military and economic agreements between the two countries for three months when Israel proved uncooperative in negotiating a second Sinai agreement). This is a scenario with which many Israelis, including Netanyahu, are unlikely to be comfortable.