Donald Trump has threatened Mexico with a 25 per cent on autos if the country stops apprehending migrants making their way to the US, just as he is set to travel to the border.

In a series of tweets, the president took a swipe at The Washington Post, and said that he would penalize Mexico in spite of the trade deal with Mexico and Canada — the United States-Mexico-Canada Agreement (USMCA) — that he has made a signature foreign policy goal in the western hemisphere.

Mr Trump continued on to claim that $500b-worth of drugs are smuggled into the US over the Mexico border a year, contributing to the deaths of 100,000 Americans each year.

"The Crazed and Dishonest Washington Post again purposely got it wrong. Mexico, for the first time in decades, is meaningfully apprehending illegals at THEIR Southern Border, before the long march up to the U.S. This is great and the way it should be. The big flow will stop," Mr Trump wrote.

He continued: "However, if for any reason Mexico stops apprehending and bringing the illegals back to where they came from, the U.S. will be forced to Tariff at 25% all cars made in Mexico and shipped over the Border to us. If that doesn’t work, which it will, I will close the Border."

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

"This will supersede USMCA. Likewise I am looking at an economic penalty for the 500 Billion Dollars in illegal DRUGS that are shipped and smuggled through Mexico and across our Southern Border. Over 100,00 Americans die each year, sooo many families destroyed!"

Mr Trump is headed to California to review a portion of border wall that has been constructed near the Calexico Border Patrol station.

"Heading to the Southern Border to show a section of the new Wall being built! Leaving now!" Mr Trump tweeted.

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The section of border wall that Mr Trump is set to visit in southern California is actually a renovated portion that the president has touted as the first portion of his new wall.

The fencing there was already built when he came into office, and plans to modernise the section were actually developed during the presidency of Barack Obama. Funding for the portion of wall was not made available until Mr Trump came into office.