President Obama vigorously defended his nuclear negotiations at the end of a summit of Persian Gulf state leaders and a rocky visit to Saudi Arabia aimed at reassuring the anxious ally and seeking more support for the fight against the Islamic State. While the president acknowledged Saudi concern that the United States should not be "naïve" when dealing with Iran, he cited previous presidents' willingness to engage in talks with Russia during the height of the Cold War as models to follow. "John F. Kennedy and Ronald Reagan still negotiated with the Soviet Union even when the Soviet Union was...