When congress issued the gulf of tonkin resolution, how did that contribute to upsetting the checks-and-balances system?

The Gulf of Tonkin Resolution was passed by the Senate on August 7, 1964 and it basically gave the president of the United States the ability to use the military forces without the declaration of war. The ability to declare war rests only on the Senate and this gave more power to the President and many think it upset the checks-and-balances system.