Why is the gulf of tonkin incident controversial? how did it johnson win the 1964 election?

The Gulf of Tonkin incident occurred on August 2 and 4, 1964 when the US Navy USS Turner Joy and USS Maddox destroyers participated in a controlling operation of the Gulf of Tonkin area in the which were attacked by four North Vietnamese torpedo boats as a retaliation for a previous strike.

Defense Secretary Robert S. McNamara presented to the Congress the evidence of the attack in order to obtain the so-called Gulf of Tonkin Resolution for which the Congress agreed to grant the President full powers to dispense with legal limitations when it came to involving the US in the war.  It was controversial because the Constitution requires Congress to declare war in order to effectively get into a state of war with a foreign nation.

This situation helped President Johnson to win the 1964 election, as it showed him as a strong president who took care about American interests abroad, earning him a strong base of support.