The Trump administration has acquired just 16 percent of the private land in Texas it needs to build the president’s border barrier, casting doubt on his campaign promise to complete nearly 500 miles of new fencing by the end of next year, according to the latest construction data obtained by The Washington Post.

And of the 166 miles of border barrier the U.S. government is planning to build in Texas, new construction has been completed along just 2 percent of that stretch a year before the target completion date, according to the construction data. Just four miles of the planned border wall in Texas is on federal land – the other 162 lie on private property.

Faced with intense pressure to meet Trump’s 500-mile campaign pledge, administration officials have instead prioritized the lowest-hanging fruit of the barrier project, accelerating construction along hundreds of miles of flat desert terrain under federal control in western states where the giant steel structure can be erected with relative ease.

That has deferred the tougher work of adding miles of fencing along the zigzagging course of the lower Rio Grande Valley in South Texas, the nation’s busiest corridor for illegal crossings. There, along the winding river’s edge, the land is almost all privately held, and the government would need to obtain it – either via purchases or eminent domain land grabs – before any construction begins.