Which of the following authorities is NOT a member of the Joint Chief of Staff?

The Chief of Staff of the United States Coast Guard is not a member of the Joint Chiefs of Staff. The Joint Chiefs of Staff primarily consists of the senior military officials from the Army, Navy, Air Force, Marine Corps, and the National Guard Bureau, with the Chairman of the Joint Chiefs serving as the principal military advisor to the President, the Secretary of Defense, and the National Security Council. The Coast Guard, while a vital branch of the U.S. military, operates under the Department of Homeland Security during peacetime and only falls under the Department of Defense during wartime or national emergency. This distinction in departmental alignment means that the Chief of Staff of the Coast Guard does not sit on the Joint Chiefs of Staff, thus confirming that this choice is the correct answer.