I figure that states would regulate their region - for example, if a president wants troops from their region, the individual states have to agree to supply the troops. This puts an onus on a regional president to negotiate terms with states and other regions if they want to do stuff. Mind, I think there would have to be an exception for natural disasters like hurricanes and forest fires, with a footnote that deployed troops have to be unarmed.

We want a certain degree of gridlock, where no one has too much authority, but not so much rigidity that nothing can be done. Kinda like how traffic lights and road layouts dictate how a city operates. Political divisions and systems are architecture designed to address chaos.