Well ok.
Speaking on a flight from Washington to Paris, Mr Trump told reporters on board Air Force One that it was vital border agents could see through the wall to be aware of oncoming dangers.
"One of the things with the wall is you need transparency. You have to be able to see through it," he said.
"So it could be a steel wall with openings, but you have to have openings because you have to see what's on the other side of the wall.
"As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don't see them. They hit you on the head with 60 pounds of stuff? It's over."
