It was admitted that people lied to Trump about the actual troop numbers so it wouldn't be reduced further.

this country is so far up the military's ass that there has been zero precedent to do so

He can pull out of all engagements sure. But the next pres will just put them back in again.

Of course not, if he tried to do something like that, God knows what would happen with his life

Yes, he has the constitutional authority to order troop withdrawal at any time, it's more a matter of a) whether he wants to, and b) his advisors/generals will almost certainly resist

Yes he can but if killing stop.Nuclear material might just fall into the wrong hands

He hasn't that much power to stop it completely and most of them don't even want to. Bider is certainly, just like his former Boss Obama, A President of War.

As a commander in chief he can order the military to do everything within the limits of constitution and laws as far as I know?

He's the commander in chief, in recent years they don't even need congress to wage war. So yes.