The events in the Gulf of Tonkin threatened the separation of powers established in the U.S. Constitution primarily by shifting war-declaring authority from Congress to the President. According to the Constitution, only Congress has the power to declare war (Article I, Section 8), while the President is designated as Commander in Chief of the armed forces (Article II, Section 2). However, after the Gulf of Tonkin incidents in August 1964, President Lyndon B. Johnson sought and obtained from Congress the Gulf of Tonkin Resolution, which authorized him to take "all necessary measures" to repel attacks and prevent further aggression without a formal declaration of war by Congress

. This resolution effectively gave the President broad, unchecked power to escalate U.S. military involvement in Vietnam, bypassing the constitutional role of Congress in deciding whether to go to war. Congress’s near-unanimous approval of the resolution meant that the President could conduct military operations with minimal legislative oversight, undermining the system of checks and balances fundamental to the Constitution

. The resolution was criticized for being a "blank check" for the President to wage war, which led to a significant expansion of executive power at the expense of congressional authority. This imbalance prompted Congress to later repeal the resolution in 1971 and to pass the War Powers Resolution in 1973, aimed at reasserting congressional oversight and limiting the President’s unilateral military action

. In summary, the Gulf of Tonkin events and the subsequent resolution threatened the constitutional separation of powers by allowing the executive branch to assume war powers that the Constitution explicitly grants to Congress, thereby weakening the checks and balances designed to prevent unilateral military engagement by the President