Withdrawing from NATO, I could see Trump entertaining that (wouldn’t actually happen).
Fire a bunch of the top leadership? For sure. That would both be something Trump could “order the military to do,” as well as something he might do, and it would also harm the US military’s capability to wage war.
Zero out Pentagon funding? Not possible for trump to do alone, but depending on the congressional make up, it could be done and would severely limit the ability of the US Military to wage war. They could even do it without affecting enlisted personnel enrollment. The Pentagon has their own funding 100% separate from military spending.
Could also deny all future discretionary spending for the military/pentagon.
If you want privacy and you drive a car, I got bad news for you. Public Transit is privacy.