U.S. President Donald Trump is headed Tuesday to the country's southwestern border with Mexico to look at 30-foot-tall prototypes of the wall he wants to build to thwart illegal immigration.Trump left Washington for San Diego, California, to see eight sample sections of walls just north of Tijuana, Mexico, that could be built along much of the U.S.'s 3,200-kilometer border with Mexico. But the $20 billion wall is controversial, and Congress has not funded it yet, as lawmakers are deadlocked over sweeping proposals to change U.S. immigration policies.Trump is likely to be greeted by rallies both for and against what he has described as a "big beautiful border wall." On Monday, anti-Trump immigrant activists chanted, "We reject your hate! We don't need your racist wall!" Others in San Diego support construction of the wall, saying the U.S. border is not secure.Many U.S. lawmakers are skeptical over the need for the wall -Trump's signature campaign proposal in his successful 2016 run for the White House. But opposition Democrats said recently they were willing to provide some initial funding for it in exchange for preventing the deportation of about 1.8 million young people who had been brought to the U.S. illegally years ago by their parents.However, immigration negotiations collapsed between the White House and Congress, leaving the issue unresolved. The immigration debate could emerge again late next week as government funding expires and Congress is faced with approving a spending plan for the remainder of the current fiscal year through the end of September. Contentious relationsTrump's trip to California along the country's Pacific coast is his first to the most populous U.S. state since he took office nearly 14 months ago. The state voted overwhelmingly for Trump's opponent, Democrat Hillary Clinton, and California officials since then have engaged in frequent disputes with the White House over Trump's populist approach to governing and his anti-immigration policies.The Justice Department last week sued the state to overturn California laws aimed at thwarting federal immigration officials in their efforts to arrest and deport undocumented immigrants, particularly those who had committed crimes, served jail sentences and were being freed after completing their terms. The Trump administration has also sought to block cities in the state from declaring themselves sanctuary jurisdictions to protect undocumented immigrants from deportation.On Monday, Thomas Homan, acting head of the country's Immigration and Customs Enforcement agency, criticized three of the state's most prominent Democrats - Gov. Jerry Brown, House Minority Leader Nancy Pelosi and Sen. Dianne Feinstein - for attacking Trump's immigration control efforts."If people don't like it, people like Nancy Pelosi and Dianne Feinstein, they can change the law. They're legislators," Homan said.After the San Diego stop, Trump heads north to Los Angeles, where he will attend a Republican National Committee fundraiser for his 2020 re-election campaign, with tickets ranging from $35,000 to $250,000.