President Donald Trump launched his 2016 campaign with a huge goal: to build a "big, beautiful wall" spanning across the nation’s southern border, paid for entirely by the Mexican government.

As it turns out, Mexico has zero interest in covering the price tag for Trump’s construction project – and it doesn’t look like the U.S. can foot the bill, either. Trump’s administration has only managed to locate $20 million of federal funding that could be redirected to support the massive construction project, Reuters reported Thursday.

A leaked Department of Homeland Security document revealed the White House has just barely enough to cover the cost for several wall prototypes – rough drafts of what a sprawling, 1,500 mile-long barrier may look like – and nowhere near the project’s estimated total cost of over $20 billion. 

RTX2SW0M A general view showed a newly built section of the U.S.-Mexico border wall at Sunland Park, opposite the Mexican border city of Ciudad Juarez, Mexico, Nov. 9, 2016. Photo: Reuters

The federal government has been searching for a way to pay for Trump’s campaign promise ever since the president signed an executive order Jan. 25 saying the border wall will be paid for with "existing funds and resources."

But it remains unclear exactly how the wall will be paid for, or when the U.S. will officially begin construction along the U.S.-Mexico border. Vice President Mike Pence said Mexico would pay for the project in an interview with "Good Morning America" Wednesday, saying the plan is part of Trump’s "agenda that a majority of Americans believe is the right agenda for the country."

Trump has walked back statements suggesting Mexico will immediately pay for the project since taking office, instead suggesting U.S. taxpayers may have to be paid back by the Mexican government for initially funding the wall’s construction.

"The dishonest media is not reporting that any money spent, for the sake of speed, on building the Great Wall, will be paid back by Mexico," Trump tweeted Jan. 6.

House Speaker Paul Ryan has said he plans on including at least a portion of the wall’s projected cost in the Congressional budget request for the upcoming fiscal year. Meanwhile, walls, fences and other security features already exist along the U.S-Mexico border, though Customs and Border Protection and local communities say such obstacles aren’t enough to curb illegal immigration, drug trafficking or human smuggling.