The biggest problem for Trump’s border wall isn’t money. It’s getting the land.

In 2008, the George W. Bush administration, which had started building about 670 miles of border fencing on mostly federally owned land in Arizona, California and New Mexico under the Secure Fence Act of 2006, tried to seize an acre or so in Cameron County, Tex., that belonged to Eloisa Tamez. Things did not go quickly.

Tamez fought the government in federal court. During seven years of litigation and negotiation, she became famous for resisting the border fence. The government eventually paid her $56,000 for a quarter-acre the fence sits on and gave her a code to open a gate so she can access her land to its south.

Imagine this playing out over and over again along the 1,300 miles of borderlands that President Trump wants to wall up. “We will soon begin the construction of a great wall along our southern border,” Trump promised Tuesday night in an address to Congress. “It will be started ahead of schedule, and, when finished, it will be a very effective weapon against drugs and crime.”

But actually building the wall, as the Tamez saga shows, won’t be as easy as dashing off an executive order requiring it. The main problem won’t even be the $25 billion that some estimates say the barrier could cost. Trump’s real difficulty will be in getting permission from property owners to build the wall — no matter how much money it takes — and the land wars that will bog down his plans.

Trump, who has cast himself as a master dealmaker, will need to coordinate massive voluntary sales of property near the border or negotiate easements for large swaths of land to make way for the wall construction. This is no small feat. Only about one-third of the land the wall would sit on is owned by the federal government or by Native American tribes, according to the Government Accountability Office. And much of that territory is already fenced. The rest of the border is controlled by states and private property owners. Estimating the costs of negotiated sales of all the territory at stake is difficult ahead of time, because the fragmentation raises questions about market value, particularly for land in the limbo zone south of the planned wall but north of the border.

[Trump is bullying Mexico because Mexico is letting him do it]

Costs aside, resistance is building. Landowners, Native American tribes, and Republican and Democratic lawmakers are on record opposing the wall. What happens if this resistance turns into outright refusal to sell land? Trump’s only option at that point would be eminent domain — which could prove to be even harder than cutting individual deals.

In trying to take land for the wall, the federal government would be held to time-consuming procedures that include consultation and negotiation with the affected parties — including private landowners, tribes, and state and local governments — before taking any action. Federal law requires the government to consult with “property owners … to minimize the impact on the environment, culture, commerce, and quality of life for the communities and residents located near the sites at which such fencing is to be constructed.” Then the government would need to declare a taking and undergo condemnation proceedings.

The Fifth Amendment’s takings clause states, “Nor shall private property be taken for public use, without just compensation.” What this means is that the government may seize someone’s property and transfer it to another governmental entity or to a private entity, but only if doing so is for a public use. A long-standing interpretation of the clause allows taking property to build highways, bridges, airports and dams. As for a wall? It would probably pass muster, although resolving that question in federal court may take time. But the problems wouldn’t end there.

The Fifth Amendment’s takings clause states, “Nor shall private property be taken for public use, without just compensation.” What this means is that the government may seize someone’s property and transfer it to another governmental entity or to a private entity, but only if doing so is for a public use. A long-standing interpretation of the clause allows taking property to build highways, bridges, airports and dams. As for a wall? It would probably pass muster, although resolving that question in federal court may take time. But the problems wouldn’t end there.

President Trump has promised to build a wall on the U.S. Mexico border. People living along the border say there will be significant challenges. (Zoeann Murphy/The Washington Post)

The takings clause also protects private landowners from uncompensated seizures. Owners who are subject to eminent domain to build the wall would have to receive compensation for its physical presence on their property. Successfully measuring the value of the land and settling on prices for hundreds of owners with unique property interests, however, would be the “deal” of the century. Determining just compensation is not easy in contested cases in which the land and property at stake are infrequently exchanged on the market. There are few other properties in the United States situated along an international boundary, some of which is already fenced, which makes fair value hard to establish.

As Eloisa Tamez’s case demonstrated, that’s a lot of ammunition for hundreds of landowners. If the rollout of Trump’s hastily drafted travel ban is any indicator, we should expect sloppy execution of statutory requirements and takings procedures if the administration attempts to condemn border land.

[Canadians want to build a wall, too — to keep Americans out]

Tribal lands would be an even bigger obstacle. Most such land in the wall’s path belongs to the Tohono O’odham Nation, including a reservation that extends along 62 miles of the border in Arizona. Tribes have certain property rights under the Constitution and federal statutes. Many of their lands are held in trusts, which federal law recognizes as independent political entities. Trump would need a bill from Congress to acquire the tribal lands, which are protected by treaties and other statutory equivalents.

What is the result of all of this? Years and years of litigation before the “immediate construction” of the wall. Any federal eminent domain action on such a large scale against even a few landowners could trigger decades of court disputes before anything is built. As Trump, a New York real estate tycoon, is surely aware, the Atlantic Yards redevelopment project in Brooklyn endured multiple condemnation challenges, resulting in six years of litigation and negotiation. before anything was built. And that was a much smaller undertaking.

As it happens, the president has plenty of experience attempting to seize land on the East Coast. He does not hide his enthusiasm for taking businesses and homes for his own business interests. In the mid-1990s, Vera Coking, owner of a house just off the boardwalk in Atlantic City, was subject to Trump’s wrath when he tried to persuade the local authorities to condemn her property so he could construct a parking lot for the 22-story Trump Plaza Hotel and Casino he had built right next door. He turned to the government-established Casino Reinvestment Development Authority after Coking refused to sell. Trump lost that battle in Casino Reinvestment Development Authority v. Banin. In 1994, Trump threatened to condemn five businesses in Bridgeport, Conn., to make way for an office and entertainment complex and, as he did in Atlantic City, lobbied city officials to exercise eminent domain. It didn’t happen.

The Supreme Court upheld the legality of takings motivated by economic-development concerns — the sort Trump championed in his real estate career — in a controversial 2005 decision in Kelo v. City of New London. The plaintiff, Susette Kelo, lost her Connecticut home in that debacle. After a legal saga that began in 1998, the end result was a failed development project.

The Great Wall of Trump could leave hundreds of Cokings and Kelos at risk of losing their property. Pressure for Trump to back down will mount; these types of land grabs spark public outrage. After Kelo, there was a state-led backlash: Within several years of the decision, most states had enacted legislation giving owners additional property protections.

Americans do not take kindly to threats to fundamental principles of property ownership, even if some of them (though not most, polling shows) like the concept of the wall and the immigration policy Trump wants to pursue. It is not inconceivable to think we are heading for another Kelo saga. The wall could lead to the backlash of the century: a resistance movement laced with political, cultural, social and economic consequences. While Kelo’s land grab was for economic development, Trump’s wall is in service of a wrongheaded immigration policy. Surely this public purpose, like the one in Kelo, will inflame the passions of Americans who see our country as a symbol of democracy and inclusion, not as an isolationist nation.