Observers disagree over the nature of United States policy toward Iran under Carter as the Shah's regime crumbled. According to historian Nikki Keddie, the Carter administration followed "no clear policy" on Iran. The American ambassador to Iran, William H. Sullivan, recalled that the US National Security Advisor Zbigniew Brzezinski "repeatedly assured Pahlavi that the U.S. backed him fully". On November 4, 1978, Brzezinski called the Shah to tell him that the United States would "back him to the hilt." At the same time, high-level officials in the State Department believed the revolution was unstoppable. After visiting the Shah in summer of 1978, Secretary of the Treasury W. Michael Blumenthal complained of the Shah's emotional collapse, reporting, "You've got a zombie out there." Brzezinski and Energy Secretary James Schlesinger were adamant in their assurances that the Shah would receive military support.