What Kerry has done, in effect, is get the two sides to grab hold of a stick of dynamite. If they can’t defuse it within nine months through an agreement, it’s going to blow up: The moderate Palestinian government in the West Bank would collapse; militant Palestinians would take statehood to the United Nations, probably this time with broad European support; an angry Arab League would withdraw its peace initiative. It would be a big mess for everyone.

Tzipi Livni, the chief Israeli negotiator, recalled at a State Department ceremony Tuesday that when she first talked with Kerry about a new round of peace talks five months ago, he told her that “failure is not an option.” By pushing the two sides into an actual negotiation, Kerry has put some teeth into that bromide. If they fail this time, it will cost the parties dearly, probably Israel most of all. That provides harsh leverage for Washington.

Kerry’s second advantage is that he’s ready to be an active broker in this deal rather than a passive listener or mediator. When the two sides reach impasses or get bogged down on side issues, Kerry will seek to break the logjam with U.S. proposals. By putting a nine-month fuse on his dynamite stick, Kerry limits stalling tactics of the sort adopted in the past by both sides.