President Donald Trump’s vision for a wall along the Mexico border will remain unfinished when he leaves office in January. The president-elect, Joe Biden, has pledged to stop construction after he is inaugurated, leaving Trump’s monumental project half-built and broken up by gaps.

U.S. Customs and Border Protection (CBP) officials and military planners at the U.S. Army Corps of Engineers have had urgent meetings in recent days to prepare for Biden’s likely stop-work order, according to officials at both agencies who spoke on the condition of anonymity because they were not authorized to discuss the conversations publicly. The officials acknowledge that the structure almost certainly will remain incomplete in areas where construction crews do not have time to wrap up their work by Jan. 20, Inauguration Day.

“We’re looking at project timelines, estimated construction completion and looking to prioritize segments of the wall to minimize the potential threats created by a stoppage,” said one senior CBP official involved in the conversations.

At several locations along the border, crews have been working around-the-clock to install as much of the 30-foot steel bollard fencing as possible before Trump leaves office and the paychecks cease. The companies will be entitled to compensation from the Biden administration for the “demobilization” costs of withdrawing crews and equipment, but the contracts have a termination clause that allows the government to break the deals, said Raini Brunson, a spokeswoman for the Army Corps, which oversees the private companies building the barrier.

“The termination clause permits the government to exercise its right to terminate the contract for its convenience,” Brunson said. “If terminated for convenience, the contractor is entitled to submit a request for termination settlement costs.”

A man passes new border wall sections, right, as they replace old fencing on Friday, Jan. 10, near Yuma, Arizona. AP Photo/Elliot Spagat

Those contracts have not been made public, and Biden’s transition officials may not learn for several more weeks what those demobilization costs could be. Also unknown is whether the government would be able to modify contracts to stop new construction while still allowing for the installation of sensors, lighting and other surveillance technology – which the Biden administration favors – along segments of the wall that already are in place.

The Trump administration has completed 415 miles, according to the latest CBP figures, and the agency says crews remain on track to complete 450 miles by the end of the year. Brunson said the Army Corps does not have an estimate as to how much more could be finished between the end of the year and Inauguration Day.

Also unclear is what the Biden administration will do with unused Defense Department funding that Trump diverted from military construction and counternarcotics programs to pay for the wall. Trump has obtained about $15 billion for barrier construction, enough to cover 738 miles, making it one of the most expensive federal infrastructure projects in U.S. history.

One-third of the money was provided by Congress, and the rest came from the Pentagon. Despite Trump’s campaign promises, Mexico has not paid for any of the wall.

Trump’s project has added just a few miles of new fencing where none previously existed. The effort largely has consisted of replacing small, older vehicle barriers with towering steel bars meant to block people.

The Biden campaign declined to respond to questions about the new administration’s immediate plans for Trump’s wall, referring inquiries to the president-elect’s website. Among the changes outlined for Biden’s first 100 days is ending the 2019 national emergency declaration that provided Trump with the mechanism to divert military funding to wall construction.

“Building a wall will do little to deter criminals and cartels seeking to exploit our borders,” the website reads. “Instead of stealing resources from schools for military children and recovery efforts in Puerto Rico, Biden will direct federal resources to smart border enforcement efforts, like investments in improving screening infrastructure at our ports of entry, that will actually keep America safer.”

Biden was more explicit during an interview this summer when he told NPR’s Lulu Garcia-Navarro that “there will not be another foot of wall constructed in my administration.”

Jessica Bolter, an analyst with the nonpartisan Migration Policy Institute in Washington, said ending Trump’s emergency declaration would be “one of the easiest actions for President Biden to take right away.” But a moratorium on all wall construction activity would be unusual, she said.

“A future Biden administration would still likely need to dedicate some funds to barrier maintenance, but if he really doesn’t construct another foot of wall, that would be a break from the past five administrations,” Bolter noted. “New border walls and barriers have been constructed under every president since at least President George H.W. Bush.”

Areas that are likely to be left with gaps and unfinished segments that end abruptly are located mostly in areas with challenging, mountainous terrain, CBP officials said.

For example, crews are blasting into the mountainsides of a rugged, roadless area in southeast Arizona called Guadalupe Canyon, where the barrier costs $41.1 million per mile. That span isn’t scheduled for completion until June 2021, meaning that it probably will end up as a gouged-out scar on the terrain – with no barrier rising from the ground.

“The heartbreaking thing is we’re watching them detonate these areas that will never be finished,” said Laiken Jordahl, who has led opposition to the project for the Tucson-based Center for Biological Diversity. “These contractors are destroying habitat for endangered jaguars in order to clear a path for a wall that will never be built. It’s just absurd.”

Jordahl said environmental groups will try to rehabilitate fragile areas damaged by the blasting, “but you can never un-dynamite a mountain and piece back together wilderness that has been blown apart.”

Construction of the barrier during Trump’s term has unfolded along divergent tracks, with most of the new fencing added in states where the land was already under federal control. In places such as San Diego; Yuma, Ariz.; and the El Paso, Texas, area, the new barriers are mostly complete.

But along the windy 1,200-mile course of the Rio Grande, which accounts for about two-thirds of the international boundary between the United States and Mexico, the Trump administration has built relatively little, despite identifying those areas in Texas as its highest security priority.

The land needed for the project along the river is almost all in private hands, and the Trump administration has spent the past several years slogging through the condemnation process in court that would allow the government to seize it. The government has obtained about 40% of the land it sought for the project, but crews have completed just six miles of new barriers in the lower Rio Grande Valley.

CBP and Army Corps officials said they don’t know what will happen to private land that the government has taken, or which federal agency might take possession of it if no barriers are built. If the government has obtained the land but hasn’t paid for it, the Biden administration could renounce its claims and return full possession to the previous owner.

CBP officials are aiming to complete an additional 30 or so miles in the Rio Grande Valley by Jan. 20, but that will leave the project far short of Trump’s targets. The agency said in a statement that it will continue to build with the funding it has obtained.

“Since the U.S. Border Patrol began constructing border barriers nearly 30 years ago, these barriers have proved to be a critical component in gaining operational control of the border and allowing for greater efficiency of manpower,” the statement said.

Ronald Vitiello, a former U.S. Border Patrol chief who was closely involved in planning for the wall, said that stopping construction and leaving gaps in the barrier is likely to funnel illegal activity to those locations, where crossers will try to sneak through and evade detection.

“There is always going to be a weak link that will be easier to cross than somewhere else,” Vitiello said. “The planned upgrades won’t occur in those areas, and they will be subject to exploitation by smugglers.”