Trump's campaign pledge to build a massive wall along the border between the US and Mexico has proven just as divisive outside Capitol Hill.
In line with promises of new gear, Trump said the US would "lead again" on the final frontier and introduced his administration's strategy for space exploration "recognizes space is a war-fighting domain".
While in California, Trump is also expected to speak to Marines in San Diego. He'll be staying there overnight.
About 10 miles (16 kilometers) west of the prototypes, protesters chanted, "No ban!"
Meanwhile, anti-Trump protesters gathered near the Plaza Las Americas mall in San Ysidro with signs including "love has no borders" and "no hate in the Golden State".
In Beverly Hills, a protest meant to "resist" Trump and planned for 5 p.m.in Beverly Gardens Park was being hosted by a group called "ICE Out of LA", according to its Facebook page.
The wall prototypes were constructed pursuant to an Executive Order issued on President Trump's fifth day in office.
"The taxes are way, way out of whack, and people are going to start to move pretty soon", Trump predicted.
"The public has been expressing a strong desire to publicly show their overwhelming support for President Trump's visit and his commitment to securing our border and homeland", said Jeff Schwilk, Founder of San Diegans for Secure Borders.
He called on Congress to "fully fund" the wall, no matter which prototype, or prototypes, were chosen.
Faulconer's remarks appeared in a commentary published in The San Diego Union-Tribune. Trump and the Department of Justice said that California was "obstructing federal immigration enforcement efforts" and filed the lawsuit. Tens of thousands of people enter the USA daily from Tijuana, Mexico, many on their way to work or school in San Diego. Trump is scheduled to visit eight prototypes for the massive wall he wants built along the USA border with Mexico. He said his organization respects free speech and hopes Tuesday's rally will be safe for participants.
The visit - Trump's first to the state as president - coincided with an escalating battle between his administration and the liberal state, which Democrat Hillary Clinton easily carried in the 2016 presidential election.
Earlier, about 250 Trump supporters rallied near San Diego's Otay Mesa border crossing.
Tractor-trailer rigs have been parked along the USA side, blocking the view from Mexico.
Not long after Trump touched down in San Diego just before noon, swarms of demonstrators rallying against his administration and his supporters were already out in full force - divided by a row of uniformed officers holding onto batons.
Construction of the eight wall prototypes in the San Diego area were completed in October of past year.
Protests are also planned across the border in Tijuana, Mexico, when Trump visits the wall prototypes built along the global border to fulfill his signature campaign promise. Trump has insisted Mexico pay for the wall but Mexico has adamantly refused to consider the idea.
Trump's visit comes just days after his Justice Department sued to block California laws created to protect people living in the US illegally.
A sign hung over a fence on the Mexican side of the border summed up the sentiment: "Trump, we will not pay for your wall".
Later, in a press briefing, flanked by members of federal law enforcement agencies, President Trump promised that the wall would save lives and money "by reducing crime, drug flow, welfare fraud, and burdens on schools and hospitals".