British Prime Minister Harold Wilson is credited for the political aphorism “a week is a long time in politics”, but it was a former White House official who warned Donald Trump that “it is easier to negotiate nuclear weapons than it is to negotiate trade.”

Last week the Post political economy team looked at the Chinese officials about to embark on a tour across the heartland farming states of Montana and Nebraska, with the promise of renewed purchases of soybeans and pork as a pre-trade talks…