Yeah, Trump would need support from Congress to basically strip them of power. Even if he could find a way to suspend their rights, they wouldnt go quietly. Then he needs support from his VP and Cabinet. If half his cabinet doesnt like it, they elevate Pence who, despite his faults, is not seen as nuts. And if Trump thinks his Generals will cooperate, well, he needs them all and he needs cooperation down the chain. And as you said, these officers dont work for the President, they work for Constitution.
If Trump was wildly popular, riding a wave of nationalistic pride and popularity he'd have more power to strip away powers and centralize things. But he's very unpopular even among the Republicans. His own VP was ready to jump over the "grab her" stuff.
Trump would never win a coup attempt politically, militarily or locally.