AP Photo

Today, the essential conditions for a peace process remain. Majorities of Israelis and Palestinians continue to support a two-state solution. It remains possible to draw a border that would give the Palestinians the territorial equivalent of the entire West Bank, while allowing Israel to incorporate the vast majority of its settlers. So far, the number of settlers living in communities that would need to be evacuated has not passed the point of irreversibility. Jerusalem is still dividable. Hamas is confined to its Gaza fortress. And Abbas, a Palestinian leader like no other before and perhaps no other to come, remains in office. By the end of Barack Obama’s presidency, however, every one of these circumstances could vanish—and if that happens, the two-state solution will...