With protests raging nearby, Donald Trump has visited a section of the US-Mexico border in San Diego to see part of the wall he has hinged his political career on building.

Mr Trump visited the border in the Otay Mesa neighbourhood, the same location he stopped at last year when he reviewed several border wall prototypes that he has prescribed as a major fix for the immigration crisis he claims is threatening American values.

The president called it "an amazing project," according to the Associated Press.

Meanwhile, hundreds of protesters gathered in Southern California to demonstrate against his visit, and to push back on the idea that any border crisis truly exists except one that Mr Trump himself has created through a crackdown on asylum seekers and families fleeing violence and poverty in Central America.

Nearly three years into his first term, Mr Trump has pushed forward with construction on his border wall, in spite of pushback from congressional Democrats who have refused to fund much of the project.

Donald Trump visits a section of the U.S.-Mexico border wall in Otay Mesa, California (REUTERS)

Instead, Mr Trump has largely relied on diverted funds from other parts of the government, including the Defence Department and the Homeland Security Department.

While Mr Trump promised that Mexico would pay for the wall, instead some $3.6 billion in military infrastructure money has been raided, undercutting projects across the US from New York to Virginia and the Carolinas. All told, US Customs and Border Protection says it has received $6.2 billion since January 2017 to build the wall.

Among those projects that have had funding taken away include an ambulatory centre in North Carolina; an engineering centre at the US Military Academy in West Point, New York; a cyber-ops facility in Virginia; a fire station in South Carolina; a central heating facility on an Air Force base in Alaska; and a Kentucky middle school.

Trump prototypes for Mexico border wall demolished in California Show all 20 1 /20 Trump prototypes for Mexico border wall demolished in California Trump prototypes for Mexico border wall demolished in California The prototypes for President Trump’s border wall are being demolished. AP Trump prototypes for Mexico border wall demolished in California The US Customs and Border protection had built the eight 30-foot tall steel and concrete models near San Diego on the US-Mexico border. Reuters Trump prototypes for Mexico border wall demolished in California A 2018 report from the Government Accountability Office found that the construction challenges presented by the four concrete models would be “extensive” and those presented by two of the other models would be “substantial”. Reuters Trump prototypes for Mexico border wall demolished in California It was intended that Mr Trump would choose his favourite of the designs after testing had been completed. AFP/Getty Trump prototypes for Mexico border wall demolished in California The President is yet to comment. AFP/Getty Trump prototypes for Mexico border wall demolished in California Each prototype cost $300,000 to $500,000 to build and they are being knocked down in order to make way for the San Diego Secondary Wall project which will see up to 14 miles of barrier being built to support the existing steel border fence. AP Trump prototypes for Mexico border wall demolished in California The new barrier will not employ the design of any of the prototypes, instead being built of the favoured steel bollards which make up the current section of the wall at San Diego. Reuters Trump prototypes for Mexico border wall demolished in California The new secondary barrier being built near San Diego. Reuters Trump prototypes for Mexico border wall demolished in California The rubble of one of the demolished prototypes. Reuters Trump prototypes for Mexico border wall demolished in California A steel wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A wall prototype made from a mix of steel and concrete AFP/Getty Trump prototypes for Mexico border wall demolished in California A wall prototype made from a mix of steel and concrete AFP/Getty Trump prototypes for Mexico border wall demolished in California A concrete wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A steel wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A concrete wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A concrete wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A concrete wall prototype AFP/Getty Trump prototypes for Mexico border wall demolished in California A digger approaches the prototype wall AFP/Getty Trump prototypes for Mexico border wall demolished in California Aerial view of the wall prototypes at the US-Mexico border after they were torn down AFP/Getty Trump prototypes for Mexico border wall demolished in California An aerial view showing Tijuana, Mexico on the left and the demolished wall prototypes on the right AFP/Getty

But despite Mr Trump’s repeated claims that the US border wall is nearing completion, there actually hasn’t been much movement on creating new wall along the border. Before Mr Trump became president, 654 miles of the nearly 2,000 miles border had some form of fencing or wall on it, and that figure has remained mostly unchanged.

Instead, new construction has largely been to replace existing infrastructure, including with larger fences, bollards, lights, and roads.

Mr Trump has overseen a crackdown on immigration into the United States, with his administration notably separating families as they cross into the United States seeking asylum.

The administration has also pushed forward with efforts to stop migrants from getting into the United States at all, asking them instead to take a number at the border and to wait until they are called for a chance to have their asylum cases heard.