Despite being a logistical nightmare, President Donald Trump is still confident that his administration can build a wall along the United States’ southern border. But what that means has changed in his six months in office. On Thursday – while on Air Force One – Trump discussed his No. 1 campaign promise with reporters, revealing that it’s not necessary to build along the entire 2,000 miles of border and the importance of having the wall be transparent.

According to the Los Angeles Times, he said, “You don’t need 2,000 miles of wall because you have a lot of natural barriers. You have mountains. You have some rivers that are violent and vicious. You have some areas that are so far away that you don’t really have people crossing. So you don’t need that.” Instead, he said that protecting the border required between 700 and 900 miles of wall.

However, as ABC News reports, almost 700 miles of wall already exists between the United States and Mexico, mostly because of the Secure Fence Act of 2006, which George W. Bush signed into law. The current wall is made up of wire mesh, post and rail, sheet piling, concrete, and chain link depending on the area.

It’s not clear whether Trump’s calculations take the existing wall into consideration, but what is evident is that Trump’s not thinking about how it will impact those trying to make it into the United States. The US-Mexico border is already incredibly dangerous and life-threatening for immigrants fleeing violence and poverty, and adding more miles of wall will likely just push them to attempt these more extreme journeys. Sean Murphy of the San Diego Police Department told Voice of America that the existing fence and barriers – because of both Bush’s Secure Fence Act and Bill Clinton’s Operation Gatekeeper – have already pushed immigrants east to Arizona, New Mexico, and Texas.

In June 2015, Trump announced his presidential campaign by vowing to build a wall between Mexico and the US in order to keep drugs and undocumented immigrants out. He made this promise the cornerstone of his campaign and said he’d make Mexico pay for it. Since then, Mexico has been adamant that it won’t pay for the structure, and the administration received plenty of pushback when it tried to allocate federal funding for the wall.

In the past, Trump stated that he wanted the wall to be build out of hardened concrete, rebar, and steel. On Thursday, he also stated that the wall must be see-through to deter drug smuggling. “As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don’t see them – they hit you on the head with 60 pounds of the stuff? It’s over,” he said, according to Wired. “As crazy as that sounds, you need transparency through that wall.”

Trump’s reasoning is dubious, but he’s once again describing something that already exists. Much of the existing fence is already see-through, and it’s not because it of drug smuggling. Chain-link fences and other see-through parts of the wall do allow the Border Patrol to see what’s happening on the other side, but according to Brandon Behlendorf, homeland security expert at SUNY-Albany, it won’t stop drugs from entering the country.

“When you’re talking about remote locations, cartels utilize other technologies,” he told Wired. “They utilize drug catapults and trebuchets. They’re launching drugs not five feet from the wall, or 10 feet from the wall, where a transparent wall would help. They’re launching it 100 feet over the all, 150 feet over the wall. No amount of transparency is going to help you in that context.”