That would be irrational. Even the UK and France spend 2% of GDP on defense, and they live under America's shield. Cutting our spending down to their level would save $400 billion/year. That's not peanuts, but that's only 1/3 of the deficit.

Having sufficient capacity for violence is indispensable for the existence of a state. You need a military so you can kill people in other countries, and you need police so you can maintain an internal monopoly on violence. You can't have state-funded preschool if you don't have a state. The Ukrainians unfortunately are learning this the hard way right now.

Re: "You can't have state-funded preschool if you don't have a state" - USA is protected by two immense oceans right and left and two huge, weak and pliable neighbors up and down. From all sides USA is well protected without spending hundreds of billions anually. About ballistic missiles threat - USA already has 1,200 nuclear warheads deployed in various forms (submarine, air force, ground silos) so MADD takes care of that.

With 2% of GDP USA would take care of all its defense needs. USA does not need 11 aircraft carrier groups, about 100 nuclear-powered submarines, about 2,000 jet fighters, only God knows how many destroyers, to protect itself.

Who would ever want to invade the US? You would be destroying nearly everything of value because half the US economy is based on financial services. And it would make middle eastern insurgencies seem like childs play compared to the 10x higher gun ownership rate with better and more modern firearms in the US with a far higher percentage of practiced shooters and veterans.