This is what lifetime appointments were intended to address. There's no incentive to rule in the president's favor. Of course, now there's the prospect of gratuity for services rendered.

Look, the president can't do something like start a war without permission from congress. Congress basically delegated that authority to the president. If the president then uses it irresponsibly (as has happened numerous times since congress made this decision) then that's the fault of congress. They can very easily pass legislation requiring a declaration of war and take that power back if they want to.