President Obama has argued that international sanctions and diplomatic pressure should be given more time before the military option is pursued against Iran's nuclear program. But that is a luxury that Israel cannot afford. The window of opportunity for a pre-emptive Israeli air strike is rapidly closing as Iran hardens its sites against such an attack.
Given the mission requirements of an Israeli airstrike on Iran, Israel could be forced to act soon. As Israel's Defense Minister Ehud Barak has warned, Israel must strike before Iran's facilities are so protected that they enter a "zone of immunity" from Israeli military action.
According to intelligence experts, Iranian nuclear sites have not yet reached a stage of invulnerability to an airstrike by Israel, yet the list of potential targets is a formidable challenge. Iran's nuclear infrastructure is dispersed to make it more difficult to attack and is hardening facilities to withstand the effects of bomb blasts.
Chief among these nuclear sites is Fordow fuel enrichment plant, believed to be buried hundreds of feet beneath a mountainside in Iran's Great Salt Desert. Once Fordow's enhanced layers of protection are put in place, the plant will be impervious to the Israeli air force's "bunker busting" bombs.
At that point, the only weapon that could conceivably penetrate such a hardened, underground target would be the U.S. Air Force's new GBU-57 Massive Ordnance Penetrator, which is many times larger than Israel's biggest bunker-busting bomb. Moreover, only American bombers are capable of carrying such a huge payload.
Given the inherent limitations of its fighter planes and munitions, Israel could at best launch a one-off airstrike on Iran's nuclear facilities with limited effects. Supporters of an Israeli airstrike on Iran point to Israel's destruction of Iraq's Osirak nuclear reactor in 1981 as evidence that such a mission can succeed. However, the Osirak raid pales in comparison to the risk and complexity of what would be required to launch an airstrike on Iran's multiple underground nuclear facilities.
If an airstrike against Iran's nuclear program has a chance of succeeding, it must be conducted by the United States. Only the U.S. military has the weapons arsenal, bomber fleet, logistics and refueling capabilities to sustain a large-scale bombing campaign.
The difficult choice for Israeli Prime Minister Benjamin Netanyahu is whether to launch a pre-emptive airstrike now. Earlier this week, Netanyahu said Iran got a "freebie" when the United States and other world powers agreed to meet May 23 for international negotiations without a precondition for Iran to halt uranium enrichment.
If Israel decides not to attack Iran, the only military option would fall to the United States. Either way, America will ultimately become drawn into a military conflict with Iran -- it's just a matter of time.
Greg Slabodkin of Kenmore is a former managing editor of Inside the Air Force, a weekly newsletter.