Standing by the prototypes for the controversial wall, Mr Trump told reporters: “The border will is truly our first line of defence.”
The Republican president is on his first visit the majority-Democrat state of California, where a lot of the resistance to his policies is based.
While standing next to the prototypes Mr Trump was accompanied with border officials, chief of staff John Kelly and Homeland Security Secretary Kirstjen Nielsen.
The £12.8bn funding for the wall has not come as quickly as supporters have hoped for after multiple immigration restrictions proposed by the Republican party slowed it down.
Mr Trump examined eight styles of walls before turning his focus onto “sanctuary cities” – areas where local governments do not cooperate with federal immigration cities to deport illegal immigrants.
In San Diego he said: “They shield criminals. You can’t do that.”
Last week, the Justice Department filed a lawsuit against the state of California for allegedly violation the US constitution by passing laws protecting illegal immigrants.
Democratic Governor Jerry Brown has accused the Trump administration of “waging a war” on his state.
US President Donald Trump looked at prototypes for the border wall
Mr Trump hit back that governor saying he has “done a very poor job running California.”
The President is expected to travel to Los Angeles next to head a political fundraiser to raise money for this 2020 re-election campaign.
His sharp comments come after he fired his Secretary of State Rex Tillerson and was replaced him with Mick Pompeo.
Mr Trump tweeted: “Mike Pompeo, Director of the CIA, will become our new Secretary of State.
California’s sanctuary policies are illegal and unconstitutional and put the safety and security of our entire nation at risk. Thousands of dangerous & violent criminal aliens are released as a result of sanctuary policies, set free to prey on innocent Americans. THIS MUST STOP!
— Donald J. Trump (@realDonaldTrump) March 13, 2018
“He will do a fantastic job!
“Thank you to Rex Tillerson for his service! Gina Haspel will become the new Director of the CIA, and the first woman so chosen.
“Congratulations to all!
In a statement to reporters the US President did admit that they “disagreed on things” and that he has a more similar way of thinking to Mr Pompeo.