It's no secret that Palestinian Authority President Mahmoud Abbas plans to lobby the U.N. General Assembly this September for a resolution that will predetermine the results of any Israeli-Palestinian negotiations on borders. He made clear in a New York Times op-ed this week that he will insist that member states recognize a Palestinian state on 1967 lines, meaning Israel's boundaries before the Six Day War.

Unfortunately, even President Barack Obama appears to have been influenced by this thinking. He asserted in a speech...