WASHINGTON – President Donald Trump completed a two-day swing through California on Wednesday by visiting the U.S.-Mexico border and claiming that recently completed border fence replacement would stop people trying to enter the U.S. illegally.

Trump, speaking to reporters, said people trying to enter the U.S. would not be able to scale the fence because it is designed to absorb heat.

“You can fry an egg on that wall,” he said during his stop in the San Diego neighborhood of Otay Mesa.

A construction worker told Trump it is tradition for visitors to sign the wall. The president obliged.

Trump, who faced criticism earlier in his presidency for shifting positions on how he thought the border barrier would be designed, used some of his most forceful language yet to defend the "bollard fence" design that also had been used during President Barack Obama's administration.

“This is the one that was hardest to climb," Trump said.

Trump claimed "20 mountain climbers" were tasked with trying to scale the structure to test its effectiveness. But, he said, “this wall can’t be climbed.”

Trump had reportedly told aides previously he wanted the wall painted black to better absorb heat. Asked about the color scheme on Wednesday, Trump said he took the advice of aides that it would be “better off letting it be a natural rust.”

Trump said “we’ll make a determination later” about painting it.

Trump, who at one point said the wall would be built of concrete, said previously that the bollard fencing allows border agents to see through its trademark slats.

The president's visit to the border came amid growing controversy over his decision to divert $3.6 billion from military construction projects to pay for barrier construction. The move came months after Trump declared a national emergency to redirect money from other federal agencies to the Department of Homeland Security for the wall.

U.S. Customs and Border Protection said last month that it has built about 57 miles of "new border wall system" since 2017, the year Trump took office. But officials have previously clarified that, as of July, those barriers replaced existing fencing and did not represent new barriers in places where they did not previously exist.

Trump continues to insist on the campaign trail that the wall is going up, but he has acknowledged the job has been difficult – blaming the slow pace on Democrats.

"We are building the wall but we are pushing it. It is like pulling teeth," Trump told supporters in North Carolina in July."

Trump last visited the border in April while traveling in California. During brief remarks then, he said the U.S. was "full" and unable to accept additional migrants. The president visited El Paso last month, but focused on mass shooting victims there, not the wall.