A version of this story appeared in CNN Business’ Nightcap newsletter. To get it in your inbox, sign up for free here . New York CNN  —  Even if the writing has been on the wall for years, breaking up is never easy. China and the US don’t often see eye to eye, but for decades, they have broadly agreed that it is better to be trade partners than trade enemies. That alliance is now hanging by a thread. And the real-world collateral damage is already piling up . The presidents of the world’s two