Donald Trump spent more than a year rousing crowds with a simple promise: "I'll build a great, great wall on our southern border, and I will have Mexico pay for that wall." As the campaign wore on, it got so he could ask "Who's gonna pay for the wall?" and the audience would roar, "Mexico!" It was fun while it lasted. But now, in the cold light of day, some facts are coming into focus: It may not exactly be a wall. It won't be paid for by Mexico. And it may not get built. Donald Trump spent more than...