It is canonical that he does not poop or pee outside his suit. His suit handles all of his evacutory responses. He does not eat, a nutritional paste is injected directly into his stomach because his esophagus is virtually destroyed. It arguably received the worst damage from the fire.
The issue is that a direct war with russia would lead to the next world war guaranteed. It may not be nuclear, but it likely will. Even if it wasnt, an invasion of russia would be possibly the most difficult, drawn out, and costly war the US has ever faced.