The presidency of Lyndon Baines Johnson began on November 22, 1963, when Johnson became the 36th President of the United States upon the assassination of President John F. Kennedy, and ended on January 20, 1969. Johnson did not have an official White House Chief of Staff. Initially, his long-time administrative assistant Walter Jenkins presided over the day-to-day operations at the White House. Bill Moyers, the youngest member of Johnson's staff, was hired at the outset of Johnson's presidency. The agency convened the Apollo 204 Accident Review Board to determine the cause of the fire, and both houses of Congress conducted their own committee inquiries scrutinizing NASA's investigation. Through it all, the president's support for NASA never wavered. If he sent additional troops he would be attacked as an interventionist, and if he did not, he thought he risked being impeached. Under the command of General Westmoreland, U.S. forces increasingly engaged in search and destroy operations against Communists operating in South Vietnam. By October 1965, there were over 200,000 troops deployed in Vietnam.