Article I, Section 8 of the U.S. Constitution establishes the power to provide for national defense. It gives Congress the specific authority to collect taxes for the common defense, declare war, raise armies, and maintain a navy.

I guess you can argue how much is spent, but cutting 2/3 would only “save” about $650 billion. That would even cover the interest cost on the trillions the socialists want to spend on free stuff.