1what action by congress allowed president johnson to expand the war in vietnam? why?

The Gulf of Tonkin resolution gave LBJ the power to send troops to Vietnam without officially declaring war. The US was desperate to try and prevent the spread of communism and congress allowed this unprecedented power to be given to the president. After the war, Congress realized that was too much power to give the president as well as the war ending in failure, and enacted the War powers act. This act limited the president's power in case of a future dispute.