The U.S.-Mexico border wall is getting built, President Donald Trump often claims. Construction is happening, he says, in spite of reluctance from Congress. And lately, Trump has attached a recurring figure to illustrate how far along he’s come on his big promise. "You see the hell we are going through trying to get the wall," he said in Panama City Beach, Fla. "We’re going to have over 400 miles of wall built, much of it is already started, by the end of next year, and we’ll conclude it pretty shortly thereafter. We’ll have the whole thing sealed up and it...