WASHINGTON — On Syria, President Obama has sometimes seemed isolated within his own administration. As the atrocities have escalated — from the shelling of neighborhoods, to airstrikes on bread lines, to the use of Scud missiles against civilians, to the likely incremental introduction of chemical weapons — the Assad regime's strategy has become alarmingly clear. Unable to retake rebel-held areas, it seeks to depopulate them, producing mass casualties, refugee flows and sectarian conflict. During the last two years, it has been reported that many of Obama's top foreign policy advisers, including David Petraeus, Hillary Clinton, Leon Panetta and Ben Rhodes, have urged more robust action to arrest Syria's downward spiral.

But Obama has firmly resisted such advice, preferring instead to gradually (and, so far, ineffectively) increase training and nonlethal support for the rebels. During his recent news conference, he again urged patience. Why has the president been so resolutely inactive on Syria?

To start with the obvious: Obama was re-elected on the promise of winding down difficult foreign commitments, not making them. Both his presidential campaigns assumed and encouraged American war weariness. And any action in Syria, no matter how limited, carries heavy historical baggage: Another confrontation with a Baathist dictator concerning weapons of mass destruction?

All this can be chalked up to Iraq War Syndrome. But Obama seems to have a larger strategy in staying on the sidelines. Insofar as there is an Obama doctrine, it is this: America has over-invested resources and attention in thankless Middle Eastern conflicts and under-invested in other places, particularly Asia. Obama's goal is to rebalance the portfolio. And Syria doesn't fit. According to Vali Nasr of the Brookings Institution, "Syria challenges a central aim of Obama's foreign policy: shrinking the U.S. footprint in the Middle East and downplaying the region's importance to global politics."

If true, Obama's tactical timidity is also the expression of a kind of strategic boldness. He is challenging the post-World War II foreign policy consensus on the geopolitical priority of the Middle East. Presidents of both parties have accepted a major U.S. role in ensuring regional stability, allowing the flow of resources, defending Israel, and, more recently, countering the rise of extremism. (The Carter Doctrine, for example, pledged the use of military force to defend American interests in the Persian Gulf.) Obama's pivot to other priorities may help explain his generally passive reaction to the Iranian Green Revolution in 2009, to the Arab Spring and to events in Syria.

Syria has been a test of the Obama Doctrine, and it hasn't fared well. It is difficult to remember now, but the initial stages of the Syrian uprising were mostly peaceful protests along the lines of Tunisia or Egypt. A sharp diplomatic and economic shove might have convinced elements of the regime to give up on the Assad family. Early military support for responsible rebels might have pre-empted sectarian conflict and marginalized the jihadists.

But having missed the moment — through indecision or ideology or indecision reinforced by ideology — Obama is left to limit the damage. His own foreign policy goals — improving the image of America in the Islamic world, focusing on Israeli-Palestinian peace, pivoting to Asia — have been badly undermined. And the moral and strategic consequences are much broader. Obama's inaction has helped create an outcome with a familiar historical ring: a civil war at the heart of the Middle East that destabilizes friendly governments, empowers jihadists, increases sectarian tensions across the region and allows Iran broader opportunities for mischief. Call it the revenge of the postwar consensus.

America should not accept the refounding of the Assad regime on a vast pile of skulls. And America should not accept the disintegration of Syria into enclaves, some of them sheltering al-Qaida affiliates. So Obama has little choice but to help the rebels to win, while helping the right rebels to win out in a post-Assad power struggle. But delay has made this task much more difficult. Civil wars, over time, tend to favor the ruthless and radical. As options for arming the rebels narrow — for fear of weapons falling into the hands of future enemies — the pressure for direct American action (particularly a no-fly zone) increases. Obama's earlier passivity now pushes him toward the very policies he wanted most to avoid.

Former British Prime Minister Tony Blair recently said: "If you intervene, it can be very tough. If you don't intervene, it can also be very tough." But if you are compelled to intervene late, after squandering some of your best options, it may be toughest of all.

Michael Gerson's email address is michaelgerson@washpost.com.