Trump pictured inspecting border wall prototypes in San Diego Tuesday.
He inspected prototypes of his proposed border wall at Otay Mesa, just yards from the border with Mexico.
Trump skewered California's Democratic Governor Jerry Brown, saying he'd done "a bad job" of running a state where the taxes were "way out of whack" and criminals were allowed to roam free in sanctuary cities.
"Every state in our Union is subject to the laws and Constitution of the United States - including California".
Trump's criticism focused on tax policy, too, with the President mentioning owning property in California.
"They're the best friend of the criminal", Trump said.
"The taxes are way, way out of whack, and people are going to start to move pretty soon", Trump predicted.
Brown has an approval rating of 62 percent in California, while Trump has a 30 percent approval rating, according to a poll from the nonpartisan Public Policy Institute of California cited by Politico last month.
"You see, in California we are focusing on bridges, not walls", Brown wrote.
California officials have defiantly refused to help federal agents detain and deport immigrants in the US illegally, and the Justice Department sued the state last week over three of its immigration laws.
Trump will visit eight towering prototypes for the wall before addressing Marines, also in San Diego, and attending a fundraiser in Los Angeles.
Kar-Jen clan at Khloe Kardashian's glitzy baby shower
Last year, she had taken to her Instagram page to announce her pregnancy. Kylie shared the first close-up photo of Stormi over the weekend.
"The state of California is begging us to build walls in certain areas", Trump said, claiming people don't talk about that.
Trump called on Congress to fund the border wall but did not say whether he would veto a measure that doesn't include a punishment for so-called "sanctuary states".
"We had people trying to scale", he said. "Yet California's leaders are in open defiance of federal law", Trump said.
President Donald Trump has landed in California at last.
Kevin Faulconer said a popular cross-border airport terminal connecting San Diego and Tijuana shows that "building bridges has worked wonders".
Trump's visit comes days after his Justice Department sued to block California laws created to protect people living in the USA illegally. Sessions said the laws, which restrict how local law enforcement can cooperate with federal immigration officials, are unconstitutional and undermine national security.
"These policies release unsafe criminal offenders to prey on innocent people, and nullify the federal law", the president said.
Trump told reporters then that he was putting himself "in great danger" by coming to the border.
Trump is expected to spend the night in the Los Angeles area before heading to the St. Louis area on Wednesday. He traveled to Laredo - one of Texas' safest cities - weeks after declaring his candidacy in June 2015. But, he said, "I have to do it". The mayor's office said Faulconer, a Republican, has been clear in his opposition to walls along the border, but he did not want to blacklist companies involved in the construction of the prototypes.
Trump went on to view more of the prototypes, before stopping once again to discuss the new structures. "When we build, we are not like saying: 'Oh, gee, I wish we did it a different way'".