ON JUNE 14TH Constitution Avenue will turn into the Champs Elysées for a day. Some 150 military vehicles, 50 aircraft and 6,600 troops will roll, fly and march past the White House to celebrate the US Army’s 250th birthday (and, coincidentally, its current occupant’s 79th). The scene will be reminiscent of the annual Bastille Day parade in Paris, which so inspired Donald Trump when he attended one during his first presidential term that he has since insisted on emulating it at home.