WASHINGTON — President Donald Trump showed off construction of part of his border wall on Wednesday during a trip to Otay Mesa, California, calling it an "amazing project" and a “world-class technology system.”

“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.

“This is the one that was hardest to climb,” Trump said. “This wall can’t be climbed.”

Trump also noted that the wall was constructed to absorb heat, making the surface hot to the touch and even more difficult for a person to scale.

“You can fry an egg on that wall,” Trump said.

His visit Wednesday, intended to highlight progress on his signature campaign promise, came in the wake of reporting that he had told aides that he would pardon those found to have taken illegal actions in an effort to build the wall.

The president also faced recent criticism that his focus on the wall might be jeopardizing national security after he diverted funds from over 50 military construction projects to pay for the wall. Earlier this week, The Washington Post reported that Trump’s wall could damage 22 archaeological sites along the U.S.-Mexico border, according to a report from the National Park Service.

When asked by reporters Wednesday if he had hoped to have more of the wall completed by this point in his presidency, Trump said that he had not, adding that “you couldn’t even” build a wall across the entire border, gesturing to natural barriers that would prevent such construction.

Trump praised Mexico for their dedication to border security Wednesday, telling reporters that “they’re paying for 27,000 soldiers.”

The president was accompanied on the trip by House Minority Leader Kevin McCarthy, R-Calif., and White House adviser Steven Miller, among others.