One morning during a spasm of violence two decades ago, with suicide bombings shattering Israel every other day, the King David Hotel in Jerusalem seemed eerily empty. Foreigners were staying away. Nobody was in the diningroom. Except for two people having breakfast: US senator Joe Biden and his aide, Antony Blinken. Dennis Ross, a veteran Middle East peace negotiator, spotted them and approached. “I know why I’m here,” Ross said. “Why are you here?” “This,” Biden responded without missing a beat, “is exactly when I should be here.” Biden’s staunch support for Israel in a time of crisis is no...