Opponents of President Trump’s “big, beautiful wall” along the Mexican border, comforted that the latest budget deal doesn’t appropriate any direct funding for construction, shouldn’t rest easy just yet.

Last week, Press secretary Spicer argued with a reporter who accused the White House of downgrading the wall to a fence; the phrase “alternative walls” was thrown around.

But neither metaphor nor budget has staunched all progress. The administration claims that increased border security and defense spending amounts to a “down payment” on said wall.

The administration and the Department of Homeland Security (DHS)—the federal agency that would be tasked with building a non-metaphorical wall—still plan to pursue the project and fulfill a key campaign promise.

But obtaining funding may be far from the most difficult hurdle to overcome for a project of this magnitude, according to analysts and legal experts.

The true test of the wall’s feasibility may boil down to property: The government only owns about a third of the land along the nearly 2,000-mile border between Mexico and the United States, and obtaining the rest would require untying a knot of legal and ownership issues.

While the government can use broad eminent domain powers—the right of the government to expropriate private property for public use, with fair payment—past border security efforts have shown that tactic to be both tricky and time-consuming.

“It will clog up the courts," Terence Garrett, a security studies and public affairs professor at the University of Texas Rio Grande Valley in Brownsville, told the Chicago Tribune. "It's just an affront to property rights."

The trouble with taking land

The border presents difficult terrain, both for seizing and, eventually, building on. Much of it is owned by wealthy landholders, especially in Texas, where they’ve built orchards, golf courses, and ranches. Some private property claims date back to centuries-old Spanish land grants.

American Indians also own extensive amounts of land along the border. In Arizona, leaders of the Tohono O’odham Nation, which controls vast swaths of border territory, have called for Standing Rock-like protests if the wall comes to pass, in part because it would split up their territory between two countries.

The Bush-era effort to build more border fencing ran into many costly eminent domain issues involved in obtaining that private property, cites the Wall Street Journal. Years after the 2006 Secure Fences Act, the U.S. government still only owns 100 miles of the 1,254-mile Texas-Mexico border. And as of December 2016, 120 cases involving eminent-domain seizure for the fence were still tied up in federal court.

How the legal battles may play out

That hasn’t stopped the government from moving ahead. Landowners began receiving legal notices from the DHS in January, according to Business Insider, offering bids for property.

The process begins with a letter of intent from the government in the form of a condemnation notice. Owners can ask for a trial, which presents the jury with the question of what is fair compensation. The federal government will surely push the national security angle, which make the cases more difficult, but they’re certain to be time-consuming.

Both sides of these legal battles appear to be gearing up for a fight: Organizations such as the Texas Civil Rights Project, a legal advocacy group, have mobilized to support landowners, while the proposed federal budget for 2018 requested funds for additional lawyers “to pursue federal efforts to obtain the land and holdings necessary to secure the Southwest border,” suggesting the administration will be ramping up requests—and likely seizures.

A recent CNN analysis of cases from the last round of land seizure cases for a border wall suggests the government usually wins, but not without a high cost: $78 million was spent on 600 parcels that covered 654 miles, and an additional $25 million will be needed to pay for unresolved transactions and litigation expenses. The U.S. Justice Department told CNN that landowners would get “fair market value,” though the network’s analysis also found that 1 in 4 owners, after disputing the first offer, received a higher payment after taking the issue to court.

Eminent domain, a favorite Trump tactic

As a real estate developer who has utilized eminent domain for previous projects (in the mid-’90s, Trump bought out a private home to build a limo parking lot for an Atlantic City casino), it’s not surprising that the president has been a champion of the use of this legal tool.

He spoke of eminent domain on the campaign trail, and also supported a 2005 Supreme Court decision that expanded the “public use” component in the Fifth Amendment’s Takings Clause, which gives local government bodies the ability to seize property from private landowners and give to a private developer.

What may be surprising is that his support pits him against many within his own party: Republicans who tend to promote private business above public ownership often view eminent domain as government overreach.

Ted Cruz tried to use eminent domain as an issue with which to tarnish Trump in the presidential campaign. And Representative Jim Sensenbrenner of Wisconsin introduced a law in 2013 banning the types of eminent domain transfers to private developers Trump favors. It may prove interesting to see how far Trump’s border wall crusade can take the issue before running into pushback within his own faction.

Certainly Texas, with its conservative, small-government history, could be a tough battleground for this issue. The potential property issues at the center of the wall-building effort are often cited as one of many issues that have made it unpopular with Texas politicians who represent border districts. Rep. Henry Cuellar (D-TX 28th District) called the wall “a 14th-century solution to a 21st-century problem.”

And it’s not just Democrats. Rep. Will Hurd (R-TX 23rd District), whose district runs along 800 miles of border, says a wall would be “the most expensive and least effective way to secure the border,” and Rep. John Carter (R-TX 31st District) told My Statesman that, “If they’re building a wall in Texas, it means they are building on private land, which means it’s harder, a lot harder.”