In 2016, Trump said he would use eminent domain to build the wall

 
“With President Trump and congressional Democrats still at odds over funding a southern border wall, the president continues to float the possibility of declaring a national emergency to secure money for it, a proposition of questionable legality that would almost certainly end up in court.

But even if Trump survives a court challenge, there’s another legal hurdle he would have to face: eminent domain.

The Washington Post’s Matt Viser reports:

There are complications to building a wall along the Texas border. The topography is challenging. A river adds additional issues. And unlike in Arizona and New Mexico, most of the land along the Texas border is privately owned, so building any structure would require taking it by eminent domain.

Litigation is still pending on behalf of some of those from whom land was taken after President George W. Bush signed the Secure Fence Act in 2006.”
 
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Rieger, JM. THe Washington Post 10 January 2019.