Saudi Arabia and Iran are in a tiff.

Saudi Arabia's execution of the Shia cleric Nimr al-Nimr sparked protests across the Middle East and, now, a diplomatic row. After Shia-majority Iran made a barely-veiled threat against Sunni-majority Saudi Arabia, and protesters stormed Saudi Arabia's embassy in Tehran, the kingdom cut diplomatic ties with the Islamic Republic, giving Iranian diplomats 48 hours to leave the country.

This latest incident is only the last twitch in the long-running Sunni-Shia great game in the Middle East. Sunni and Shia, Saudi Arabia and Iran, are vying for dominance in the region.

Saudi Arabia wouldn't be so concerned if it weren't so terrified. Iran has turned Iraq into a vassal state, and the tides of the Syrian civil war seem to be turning in favor of Iran's ally, Syrian President Bashar al-Assad, now that Russia is behind him. It looks increasingly like Assad is the only alternative to ISIS. And the United States' nuclear deal with Iran arguably emboldens the Shia state further, by boosting its economy and probably (in the mind of the Saudis) hastening its march to the bomb.

All of this puts the United States in a bind. Until recently, it was no secret where the U.S. stood in the Sunni-Shia rivalry: on the side of the Sunnis. Saudi Arabia, a totalitarian state, is a key ally, and Iran is vehemently opposed to the U.S. Now, it looks like the U.S. might be trying to play off both sides against the other.

In any case, Saudi Arabia is terrified. It's hard to shed any tears over one of the vilest regimes on the planet, which also happens to be one of the wealthiest. Still, it poses the question: What is the United States policy in the Middle East?

The U.S. has two overriding strategic goals: to keep Israel safe and maintain the security of the world's oil supply. Because of these goals, it generally tries to stabilize the Middle East. If those are the country's goals, then it makes sense to ally with most of the Gulf monarchies against Iran. Iran has some oil, but less than the rest of the Middle East, and Iran continues to threaten Israel. But in terms of rule of law or human rights, Iran isn't really that much worse than Saudi Arabia or Syria. At least the original U.S. goal, to replace the Assad regime with Sunni radicals, while it would have wiped out religious minorities, made more sense than the current plan to ignore the regime and hope the problem solves itself. (In the Middle East, problems never go away. They turn into worse problems.)

Still, it's hard to know what the U.S. should do. One policy would be to admit that corrupt dictatorships probably do breed terrorism and work to promote regime change in the Middle East. Democracies are probably too ambitious a goal, but efficient, relatively-humane autocracies, in the mold of Rwanda and Singapore, might work pretty well to promote U.S. interests. In terms of religion, it would be a good idea to promote, instead of Wahhabism and Salafism, a form of Islam conservative enough to be accepted by the masses, but not violent or anti-Semitic. But that's the sort of strategy that requires the sort of long-term vision and talent in execution that's difficult for democratic governments to execute.

But it's not impossible. Maybe it's finally time for a serious U.S. strategy in the Middle East.