Proposed rewrite to cover enormous glaring plot hole.
(SPOILER WARNING)
NATHAN: You go off the reservation, I will not come after you.
TOM looks hurt, betrayed at this admission.
NATHAN: I'm just kidding, man. You go off the reservation, I'll do everything in my power to get you out of trouble. I'll forge my superior's signature, I'll irresponsibly use CIA and American military resources, I'll ruin myself financially. I will throw away my long and distinguished career, and possibly that of everyone I've ever worked with. I'll even go so far as to start an international incident--yes even risk putting our nation at war for you. Understand?
TOM: Gee, thanks, buddy. Can I buy you a latte?
NATHAN: Only if it's more than twelve years old!
The two laugh uproariously, then leave the rooftop, arm in arm.