Almost 200,000 cars, trucks and pedestrians cross between Tijuana and San Diego each day. (ABC News: Stephanie March)
At the Otay Mesa border, trucks from Mexico rumble slowly across carting everything from auto parts, to food, to pacemaker parts destined for American hearts.
The roads and bridges that link Tijuana and San Diego create the busiest land border crossing in the Western Hemisphere.
Almost 200,000 cars, trucks and pedestrians cross back and forth each day.
If Donald Trump ends up scrapping the North American Free Trade Agreement (NAFTA) between the US, Mexico and Canada, this region would be hit hard.
The deal is currently being renegotiated but Mr Trump says he will terminate it if it cannot be revised to provide more benefits for the US.
“The uncertainty doesn’t help in business planning,” says Ernesto Lozano, the CEO of freight company Mexamerica which runs dozens of trucks daily from Tijuana to the US.
Ernesto Lozano says Mr Trump’s anti-Mexico rhetoric has been damaging to business. (ABC News: Stephanie March)
Mr Trump has accused Mexico of taking manufacturing jobs away from the US but Mr Lozano says the reality is more complicated.
“This feeds a whole bunch of trucking companies, warehouses, brokers, retailers, distribution centres in California, that ship worldwide,” Mr Lozano says, pointing to a sprawling industrial complex over the border in Tijuana.
Beyond the NAFTA renegotiation, he says Mr Trump’s anti-Mexico rhetoric has also been damaging.
“What worries anybody here in business on the border is just the negative publicity that it can give and making it unattractive for businesses to come and relocate here on the border,” he says.
“Build bridges, not walls — that is our motto here at the border.”
Trucks from Mexico cross the border, bringing in everything from auto parts, to food, to pacemaker parts. (ABC News: Stephanie March)
White House rhetoric shoos away Mexican customers
In San Ysidro, on the US side of the border, a shopping mall abuts the barbed wire border fence. Armed border agents patrol metres from coffee shops and retail outlets.
“For us going into another country is like crossing the street, I mean literally it is crossing the street,” says Jason Wells, the executive director of the San Ysidro Chamber of Commerce.
He says 95 per cent of the customers that use the mall are from Mexico and that foot traffic has fallen significantly in recent months.
“A lot of people have stopped crossing … based on the fear, based on the rhetoric that is coming out of the White House,” he says.
“Everyday we are hearing things like, ‘oh they are going after people with certain types of visas’, or ‘they are checking everyone’s cell phones’, or ‘they are going to take your visa away’.
“Instead of having a government that serves the community we are having to fight against what is coming out of the Government.”
Tax on US-Mexico trade would ‘start a war of retaliation’
The US Chamber of Commerce estimates 6 million US jobs depend on trade with Mexico.
People on both sides of the border breathed a sigh of relief when Mr Trump announced he was not going to scrap NAFTA outright.
There is cautious optimism the pact’s renegotiation could lead to a better deal for all three nations and will give them a chance to accommodate sectors that didn’t exist when it was written 23 years ago.
But if Mr Trump and the Republican-controlled Congress push forward with other controversial measures — like a 20 per cent border tax for goods entering the US — experts warn that could end up hurting US workers and businesses.
“You start a war of retaliation,” says Denise Ducheny, a former California state senator and current senior fellow at the US Mexico Studies Centre in San Diego.
Earlier this year Mexico considered a boycott of US corn imports in response to Mr Trump’s rhetoric.
“[Mexico] sent their President to Brazil and Argentina to make new deals to see if Brazil and Argentina could meet their needs rather than Nebraska and Iowa,” Ms Ducheny says.
“They are going to continue to trade with others and in some ways become less dependent on the US as a trading partner.”