“I think really the success is going to be when the wall’s built, when the human traffickers can’t come through,” Trump said, speaking to reporters during the quick visit to the border after a day of fundraisers in California. “This is certainly a tremendous national emergency,” Trump said, repeating disputed claims about the threat level at the southern border.

During the tour, Trump praised the wall’s features, encouraging TV cameras to get an up-close picture of the slats, which officials said were constructed out of steel and concrete. “Virtually impenetrable,” Trump described them. Trump also claimed that three other countries were currently studying the U.S. border wall but declined to name them.

Trump said that 20 world-class mountain climbers tested different prototypes of the wall and the one he visited Wednesday was the most difficult to climb.