Just as that aircraft carrier went the wrong way when Trump ordered it to Korea, that wall he wants to build on the Mexican border, appears to be in the wrong place. Mexicans are leaving to go back to Mexico and a wall could only serve to keep them in. The influx of illegal immigrants is coming from Asia which the Mexican border wall does nothing to address.
Trump, however, is more business savvy, and knows all that but also knows how a wall will be a challenge for small drug dealers but not for sophisticated and well financed really big dealers who can afford tunnel engineers. Keeping out competition is what walls are good for.