For decades, presidents from both parties have quietly distributed a portion of these cushy posts (often in the touristy capitals of Europe and the Caribbean) to some of their most generous campaign donors. “We’re the only country in the world that does business in this way,” says Dennis Jett, a retired ambassador, career foreign service officer and professor who wrote the book “American Ambassadors.” “Nobody else has an open market on ambassadorships. The fact that nearly every modern president has done the same would seem to be the rare piece of evidence in support of Mr. Trump’s claim that he is no more corrupt than the Washington “swamp.” The incoming Biden administration now has a chance to prove him wrong. 