Even with all the turmoil in the Middle East, foreign policy is unlikely to have a decisive impact on the outcome of the U.S. presidential election. But the outcome of the presidential election will have a profound impact on U.S. foreign policy. Nowhere is that more consequential than the debate over whether, when, and with whom we go to war against Iran.

Both Barack Obama and Mitt Romney are committed to preventing Iran from obtaining a nuclear weapon that would introduce a dangerous new dynamic into an already combustible region and threaten the survival of our ally Israel. Both have indicated that they are prepared to use military force if necessary. But there are critical differences that derive from differing perspectives of the United States and Israel.

The first is when military action would be necessary and appropriate. Israel's sense of vulnerability is informed by history, geography, and Iran's malevolence. But its capabilities to inflict long-term damage to hardened underground nuclear facilities in Iran are more limited than America's. The Israeli trigger of Iran's entry into a "zone of immunity" (when these facilities become invulnerable to Israeli attack) occurs earlier than it does for the United States, giving us a longer window to act effectively. That is why President Obama has said that we still have time and space to determine if negotiations and sanctions can work.

Israeli Prime Minister Benjamin Netanyahu, on the other hand, says that that time has run out for negotiations and patience. As he reiterated in high-profile appearances on Meet the Press and other Sunday talk shows, his argument is that the United States must set forth "red lines" for the Iranian nuclear program that will provoke a U.S. military attack if crossed by the Iranians. There are arguments for "red lines" (enhancing deterrence) and against them (war on autopilot). But Netanyahu's public insistence on a U.S. declaration of "red lines" is counterproductive. Deterrence against Iran, which gains strength from perceived unity, is undermined by public discord.

Romney agrees with Netanyahu -- the time for talking is over. Negotiations have failed. We need to get tougher on Iran. But given the fact that a bipartisan Congress and the president already have imposed the harshest sanctions ever on Iran -- oil exports and nearly all banking transactions -- it is hard to know how to ratchet them up much further without a deadly squeeze of average Iranians. Given the former governor's view that negotiations are exhausted and that there should be no distance between United States and Israel on Iran, a President Romney would have us on the precipice of war -- sooner rather than later. And if we are seen by the international community as acting precipitously, we will be largely on our own.

War may come under President Obama as well. Although the administration is reluctant to embrace the double-edged sword of "red lines," any action that demonstrates a clear move toward developing a bomb -- such as throwing out the IAEA inspectors, revelations about other secret nuclear facilities, clear and sustained evidence of enrichment above 20 percent, or further weaponization -- can be expected trigger a U.S. military response. But Iran might not take such steps, soon or ever. In the meantime, the cumulative pressure of harsh sanctions and the possibilities of creative diplomacy hold out the promise of a pathway between war and capitulation. And if war becomes our only choice, the world will see that we truly have exhausted all other avenues, that it is the last alternative and that we do not take lightly the prospect of introducing another American-led bombing campaign into a Middle East already in turmoil.