The Gulf of Tonkin Resolution was significant to the Vietnam War because d) it authorized the President to use military force in Vietnam without asking Congress for a declaration of war.
This resolution, passed in August 1964 following reported incidents of attacks on U.S. naval vessels by North Vietnamese forces, gave President Lyndon B. Johnson broad authority to escalate U.S. military involvement in Vietnam, ultimately leading to a significant increase in troop deployment and military operations in the region. The resolution effectively bypassed the traditional requirement for congressional approval for military actions, which set a precedent for future conflicts.