Palestinian President Mahmoud Abbas addresses the 69th United Nations General Assembly at United Nations Headquarters in New York, September 26, 2014. (Mike Segar/Reuters)

THE GOOD news from the Middle East is that the truce between Israel and Hamas in the Gaza Strip has held for a month, and Hamas appears ready to make concessions to avoid a resumption of fighting. Last week the Islamist movement renewed its agreement with the secular Fatah party to turn over Gaza’s government and security control of its borders to the West Bank-based Palestinian Authority. Though it’s not clear that the accord will last, Hamas is emerging as the loser of the summer war. According to Israel, as much as 80 percent of Hamas’s military arsenal has been destroyed, and its poll ratings among Palestinians are sinking as it fails to deliver the gains it promised from the conflict.

Hamas’s diminution might seem to create new possibilities for agreement between Palestinian Authority President Mahmoud Abbas and Israeli Prime Minister Benjamin Netanyahu. Mr. Abbas, after all, denounced Hamas’s embrace of carnage and refused to support a simultaneous uprising in the West Bank. Yet Mr. Abbas delivered a bridge-burning speech to the U.N. General Assembly last week, mendaciously accusing Israel of “a new war of genocide” and declaring that a return to negotiations was “impossible.”

For several years Mr. Abbas has oscillated between half-hearted participation in peace talks and attempts to advance the Palestinian cause through unilateral action at the United Nations. The latter initiatives have no chance of substantive success and risk being self-defeating, as the Palestinians should have learned from Mr. Abbas’s last such gambit in 2012. Then their lobbyists were unable to win enough support for a U.N. Security Council resolution even to force a U.S. veto, and a compensatory symbolic measure in the General Assembly provoked Israel to impose painful financial sanctions.

Mr. Abbas nevertheless is trying the Security Council again, after refusing to respond to a U.S. framework for peace talks painstakingly developed by Secretary of State John F. Kerry. He proposes a resolution that would mandate the creation of a Palestinian state based on Israel’s 1967 borders in a set period of time; when it is voted down or vetoed by the United States, the Palestinians hint that they will seek a war crimes investigation of Israel by the International Criminal Court. That, in turn, would almost certainly prompt retaliatory sanctions by Mr. Netanyahu’s government and possibly by Congress, which supplies the Palestinian Authority with much of its funding.

Mr. Abbas has repeatedly rejected violence, and he has convinced a series of U.S. and Israeli negotiators that he has a realistic view of the terms for a Palestinian state. Yet he has now rejected platforms for a settlement on two occasions from two U.S. presidents. He persists in grandstanding gestures that he must know will only delay the serious negotiations that must precede the creation of a Palestinian state and that undermine those in Israel who support such talks. He has spoken for years of retiring but, at 79, he clings to his post four years after his elected term expired. Hamas has done the most harm to Palestinians and their cause in recent years. But Mr. Abbas has done little good.