When President Barack Obama hosts Turkish Prime Minister Recep Tayyip Erdogan at the White House on Thursday, their talks about Syria will have a fresh urgency. On Saturday, car bombings in the Turkish border town of Reyhanli killed at least 50 people. The Erdogan government blamed the Bashar Assad regime in Damascus for the attack.

Assad’s ouster is desperately desired by both leaders, and they will no doubt focus on this objective, particularly the question of a no-fly zone that Mr. Erdogan seeks. But a fundamental concern gets little attention because it seems so distant and difficult: What kind of Syria do they want to emerge from the massive destruction, and what is a realistic way of achieving it?

U.S. national-security interests are at stake in Syria’s civil war. Along with the possibility of chemical or other weapons of mass destruction being seized by terrorists in the chaos, these security concerns include thwarting Iran’s aspirations for regional hegemony, an aim reflected in Tehran’s support for Assad. The U.S. also wants to deny violent extremists another haven.

Yet the benefits of deposing Assad could prove short-lived if his repressive rule is replaced with another form of oppression or an unstable failed state. Syria is riven by ethno-sectarian fissures and is now a part of the larger regional strategic competition between Sunni and Shiite Muslim blocs. Assad’s removal by itself will not heal the increasingly sharp divisions in Syrian society, or prevent foreign forces from meddling and encouraging irredentist or other divisive movements.

To keep Syria together, a political transition must create a central government able to lead the entire country, but inclusive enough not to alienate frightened minority groups, which may by then include Assad’s Shiite Alawites in a majority Sunni country. Given the immense difficulty of this task, analyzing and planning for it should begin now.