Even the great wall of China was defeated by the Mongol Hoards. With todays technology Trumps wall we be easily defeated unless it's built deep enough under the ground so you can't just tunnel under it. Unless it's thick enough to survive a bomb. High enough to not be able to fly over. It would have to stop ships or boats from coming in on our coasts.
No wall can do all those things and still be affordable to build. Plus it would need an army to just maintain it. Trumps wall is a propaganda tool nothing more to give people a false sense of security