Let's face it: When Barack Obama said in Cairo that "the only resolution" of the Israeli-Palestinian conflict is two separate states, he was courageously insisting -- well, on what's become conventional wisdom.

But not the unanimous wisdom. The hardliners on each side aren't alone in questioning the two-state idea. On the street in Jerusalem, I've run into old friends, veterans of Israeli peace and human-rights activism who say we've passed the tipping point: There are too many settlements; Israeli withdrawal is impossible; negotiations on two states have repeatedly failed; the only solution is a single, shared Jewish-Palestinian state. I've heard Palestinian intellectuals, former supporters of a two-state solution, who say the same. Among writers outside the conflict zone,...