MARY LOUISE KELLY, HOST:
President Trump often tells his supporters he is delivering on his signature campaign promise. Here he is at a rally in Milwaukee this week.
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PRESIDENT DONALD TRUMP: You're going to have a wall like no other. It's going to be a powerful, terrific wall.
KELLY: That promise comes at a cost. As NPR's John Burnett reports, it is already the most expensive border wall in the world, and the bills keep piling up.