SAN DIEGO • US President Donald Trump, on his first trip to California as President, warned there would be "bedlam" without the controversial wall he wants to build on the border with Mexico, as he inspected several prototype barriers.
On the other side of the border, a small group of anti-Trump protesters vented their frustration, and announced plans to boycott United States businesses over the frontier.
"For the people who say 'no wall'... If you didn't have walls over here, you wouldn't even have a country," Mr Trump said near the border in San Diego on Tuesday.
Mr Trump repeated his insistence that law enforcement personnel should be able to see through the structure so that they could monitor criminal cartels that might be "two foot away" on the Mexican side.
"Without a wall, there would be bedlam, I imagine," he added.
Mr Trump inspected eight 9m model walls made of concrete and steel, erected side by side in Otay Mesa, an area in southern San Diego along the border with Tijuana, Mexico.
Each prototype costs more than US$300,000 (US$393,000) and, according to some estimates, the complete wall could carry a US$20 billion price tag.
Congress has yet to approve the funding amid scepticism and Democratic opposition, but an administration official said the wall would save far more money than it cost.
"Congress must fund the BORDER WALL," Mr Trump tweeted after leaving the border.
Residents in Tijuana laughed off the idea that the monolithic slabs will stop desperate immigrants.
"The wall is just a waste of money. People will continue to cross here, there, and everywhere," said resident Salome Pacheco.
The border with Mexico stretches nearly 3,200km and about one-third of it already has some type of barrier or wall.
During his visit, Mr Trump took aim at so-called "sanctuary cities" in California, where local governments refuse to cooperate with federal immigration officials seeking to deport illegal immigrants.
He said sanctuary cities nullify federal law and violate the United States' Constitution.
"They shield criminals. You can't do that," he said.
Mr Trump also slammed California's Democratic Governor Jerry Brown, saying he had done "a terrible job" of running a state where the taxes were "way out of whack" and criminals were allowed to roam free in sanctuary cities.
He said he had seen estimates that the "intolerably high" illegal immigration costs came to US$100 billion a year in terms of drugs, crime, education and social services.
Mr Trump's insistence that Mexico pay for the wall has soured relations and Mexican President Enrique Pena Nieto recently cancelled plans to visit Washington.
"I have a great relationship with the President of Mexico, a great guy," Mr Trump said, adding that "we're trying to work things out."
AGENCE FRANCE-PRESSE, REUTERS