President Donald Trump wants to build a wall between the United States and Mexico. Hundreds of miles of fence are already in place along that border, but there are no barriers on most of its nearly 2,000 miles. This episode of Reveal explores the political, logistical and geographic barriers that could get in the way of the president’s plan.

We focus first on where the physical barriers are. Applications developer Michael Corey created a digital map of every mile based on open source mapping tools and documents obtained through the Freedom of Information Act. He joins reporter Katharine Mieszkowski at the boundary between Texas and Mexico, where they explore where the border is (and isn’t), where additional walls could go up and where problems are most likely to happen.

From there, reporter Andrew Becker takes us on a tour of the California-Mexico border, where a Border Patrol agent describes how the fence has changed the landscape between the two countries and a veteran human smuggler in Tijuana explains why a fence doesn’t matter. Becker also travels to the Arizona border to interview a rancher who says the government needs to get serious about border security — but a wall may not be the answer.

So that led us to we ask: Even if a wall is built, will it matter? Other countries have erected similar barriers. Trump often points to Israel for proof that walls can keep unwanted people out. Israeli companies that make high-tech border barriers are eyeing the U.S. government as a potential huge new customer. Reporter Emily Harris, with help from producer Mark Baker, looks closely at Israel’s walls to determine whether they succeed in doing what Trump claims they do.

Finally, we consider the potential toll of a wall on wildlife and human beings.

Conservationists have conducted a handful of small studies on the effects of the border fences on wildlife. They all found the same thing: By chopping up habitats, these barriers make it harder for animals to find food, water and mates. Our story is from Texas Tribune reporters Kiah Collier and Neena Satija.

And through the story of a man who went missing as he tried to cross into the U.S. via a remote desert without a fence, reporter Stan Alcorn examines the consequences of such barriers for people on both sides of the border.

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