The war is now being waged by petty warlords and dangerous extremists of every sort: Taliban-style Salafist fanatics who beat and kill even devout Sunnis because they fail to ape their alien ways; Sunni extremists who have been murdering innocent Alawites and Christians merely because of their religion; and jihadis from Iraq and all over the world who have advertised their intention to turn Syria into a base for global jihad aimed at Europe and the United States.

Given this depressing state of affairs, a decisive outcome for either side would be unacceptable for the United States. An Iranian-backed restoration of the Assad regime would increase Iran’s power and status across the entire Middle East, while a victory by the extremist-dominated rebels would inaugurate another wave of Al Qaeda terrorism.

There is only one outcome that the United States can possibly favor: an indefinite draw.

By tying down Mr. Assad’s army and its Iranian and Hezbollah allies in a war against Al Qaeda-aligned extremist fighters, four of Washington’s enemies will be engaged in war among themselves and prevented from attacking Americans or America’s allies.

That this is now the best option is unfortunate, indeed tragic, but favoring it is not a cruel imposition on the people of Syria, because a great majority of them are facing exactly the same predicament.

Non-Sunni Syrians can expect only social exclusion or even outright massacre if the rebels win, while the nonfundamentalist Sunni majority would face renewed political oppression if Mr. Assad wins. And if the rebels win, moderate Sunnis would be politically marginalized under fundamentalist rulers, who would also impose draconian prohibitions.

Maintaining a stalemate should be America’s objective. And the only possible method for achieving this is to arm the rebels when it seems that Mr. Assad’s forces are ascendant and to stop supplying the rebels if they actually seem to be winning.

This strategy actually approximates the Obama administration’s policy so far. Those who condemn the president’s prudent restraint as cynical passivity must come clean with the only possible alternative: a full-scale American invasion to defeat both Mr. Assad and the extremists fighting against his regime.

That could lead to a Syria under American occupation. And very few Americans today are likely to support another costly military adventure in the Middle East.

A decisive move in any direction would endanger America; at this stage, stalemate is the only viable policy option left.

Edward N. Luttwak, “In Syria, America Loses if Either Side Wins”, The New York Times (25 August 2013), SR 4.