The world’s best-known secret has finally been revealed: the United States and Israel do not see eye-to-eye on Iran’s nuclear program.

In an unusually public ping-pong, the Obama administration rebuffed an Israeli effort to clarify America’s Iranian “red lines,” the point at which it would agree that its negotiations-cum-sanctions strategy has failed and it would take military action to stop the Iranian nuclear project.

Rather than attempt to resolve the issue behind closed doors, Secretary Clinton brushed off the Israeli salvo, saying "we’re not setting deadlines," a message reiterated by her spokesperson, who called the setting of any redlines "not useful." Prime Minister Netanyahu was irate, implying that the United States didn’t "have a moral right to place a red light before Israel" if it was unwilling to set red lines. Israeli ambassador Michael Oren seemingly wondered if the administration thought Iranians were color-blind. On the dais of the UN General Assembly, Netanyahu actually brandished a Sharpie pen and literally drew a red line through a cartoon diagram of an Iranian bomb. The most Obama would muster was that "time is not unlimited."

The Persian gulf between Obama and Netanyahu, however, is unrelated to their different personal convictions, political ideologies or domestic situations. Instead, the United States and Israel historically have had vastly different nuclear-proliferation policies.

Whereas the United States has never taken preemptive military action to end a country’s nuclear program, Israel always has done what was necessary to stop nuclear weapons from falling into the hands of enemy states. From Truman to Bush, Democratic and Republican presidents alike have had opportunities to prevent hostile states from acquiring nuclear weapons and yet each time did not order military action. Meanwhile, Israeli leaders, from across the political spectrum, have often taken unilateral military action to forestall regional nuclear proliferation. Regardless of who occupies the White House in 2013, the United States is unlikely to veer from over six decades of nonaction in the face of nuclear proliferation.

Over the course of the Cold War, U.S. presidents considered using hard power to stem the spread of the atomic bomb but each time recoiled at the thought of preventive military action. In the years after World War II, when the United States had a nuclear monopoly, General Douglas MacArthur, among others, advocated for a strike on Soviet nuclear installations before the Soviet Union achieved nuclear parity. Two decades later, as the United States learned of the Chinese bomb program, presidents Kennedy and Johnson seriously considered preventive military action—including joint action with the Soviet Union—before ultimately acquiescing to Chinese nuclear status in 1964. And while the Clinton, Bush and Obama administrations have played a two-decade cat-and-mouse game with Pyongyang, the ultimate result is that North Korea remains a nuclear state.

Recent history further underlines U.S. nonaction in the face of proliferation threats. When Israeli prime minister Olmert approached Washington with evidence of Syrian nuclear proliferation and asked that the United States take out the reactor, President Bush declined, offering to bring the matter to the attention of the IAEA instead. Despite having diplomatically and economically isolated the Assad regime for its support for terrorism in Lebanon and Israel as well as the insurgency in Iraq, President Bush, perhaps feeling burned by the faulty intelligence about Iraq’s nuclear program, was unwilling to use U.S. military power to uphold his nonproliferation policy’s central tenet.

On the other hand, Israel’s nonproliferation policy has been clear and unequivocal: no hostile state is permitted to acquire nuclear weapons. Despite heavy opposition from the Reagan administration, Israel, under a right-wing government, bombed Iraq’s Osirak reactor in 1981, only to be lauded by Secretary of Defense Cheney a decade later during the Gulf War. Similarly, five years ago, after President Bush demurred from attacking the Syrian reactor at al-Kibar, Prime Minister Olmert, leading a Center-Left coalition, ordered an aerial assault on the facility. (Imagine nuclear weapons in the hands of the Assad regime today.) Today, there is no Left-Right Israeli divide on Iran. At one point or another, every large political party has been part of Prime Minister Netanyahu’s coalition, and Israelis are united in their belief that they cannot live with an Iranian bomb.

No matter who wins the election on November 6, the United States will not lead any major military action to end Iran’s nuclear program. While there are indeed differences between President Obama’s and Governor Romney’s views on Iran—and those differences could have dramatic consequences on the future of the region—neither man is likely to take military action. The United States may well be able to prevent a nuclear Iran through other means, such as robust support for domestic opposition and dissident groups or cyber warfare and sabotage operations. But if Iran can overcome these obstacles, Israel should know that on Iran, the United States will not lead, whether from the front or from behind.

Gabriel Scheinmann is a PhD student at Georgetown University and a visiting fellow at the Jewish Institute for National Security Affairs.