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As Republican presidential candidate Donald Trump prepares to give a major address to bring clarity to the confusion surrounding his immigration proposals Wednesday night, one Trump position that has remained constant is his penchant for a “big, beautiful wall.”

Despite the ongoing effort and money poured into patrolling the nation's 1,989 mile southern border across rugged terrain, Trump insists he will do it better with one big wall — that he promises Mexico will pay for — to stop anyone from illegally crossing into the United States.

What Trump never mentions is that American taxpayers have already spent billions of dollars on border security, including a 700-mile long physical barrier along the southern border with Mexico.

Over the past 24 years, the amount of money spent on border security has increased 14 times; the number of border patrol agents have increased 500 percent; the amount of border wall has grown from 77 miles to 700 miles since 2000; and the number of people being apprehended trying to cross the border have decreased by four-fifths.

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It's not continuous and was built in sections to accommodate — or divert — high trafficked border crossings, but the physical barriers already exist.

A steel wall interspersed with double fencing was built along the California border separating Tijuana and San Diego that now extends into the Pacific Ocean.

Arizona has 123 miles of pedestrian fencing and 183 miles of vehicle blockades. Durable "anti-ram" fencing extends six feet under ground and 15 feet into the air to deter tunnel smugglers in Nogales. Texas is also home to 123 miles of a pedestrian fence.

These structures have not only made it difficult for smugglers and immigrants to cross, but it's made it difficult for people who live in border towns who used to cross freely for commerce, school and family.

David Taintor / Department of Homeland Security

The increase in border security funding started after the September 11, 2001 terrorist attacks. Fear of infiltration of foreign enemies spurred Congress to increase its spending on border and port security. Funding for the border jumped from $1.1 billion in 2001 to $1.5 billion in 2003.

Five years later, Congress attempted to pass comprehensive immigration reform, which would have increased border security and provided the estimated 11 to 12 million people living in the country illegally with a path to citizenship. While the bill failed, politicians’ commitment to secure the borders – mostly the southern border – did not.

Every appropriations bill has included money to secure the border. So much so that funding increased from $1.5 billion in 2005 to $2.3 billion in 2007 — eventually increasing to $3.8 billion in the 2015 fiscal year.

In 2013, Congress again tried to pass immigration reform. Again the effort failed. The border security proposals of that so-called “Gang of Eight” bill would have increased dramatically, doubling the number of full-time border patrol agents to more than 38,400. It also would have added to the construction of a physical border, including double fencing. And it would have added to the amount of virtual security like drones and mobile surveillance.

That bill would have set aside a whopping $46.3 billion over ten years to move toward the more militarized border. But with the federal government now spending nearly $4 billion per year on border security, it’s not much less than what the Gang of Eight would have hoped.

Donald Trump has not yet said how much his border security plan would cost or how he would ensure that Mexico pays for it but the American taxpayer is already shelling out a hefty amount to secure the nation's southern border.