WASHINGTON — It has become the topic of the season at Washington dinner parties and receptions. Where would you go if it really happens? Portugal, says a former member of Congress. Australia, says a former agency director. Canada, says a Biden administration official. France, says a liberal columnist. Poland, says a former investigator. They’re joking. Sort of. At least in most cases. It’s a gallows humor with a dark edge. Much of official Washington is bracing for the possibility that former Pr