The Trump administration currently has funding to build just seven miles of a promised wall along the U.S.-Mexico border, according to a new report.

U.S. Customs and Border Protection (CBP) currently has $20 million for the structure, ProPublica reported Thursday. The report said the agency's top contracting official revealed the amount during a conference in San Antonio this week.

But it's only a drop in the bucket. The U.S.-Mexico border runs for 2,000 miles. Trump's proposal for a wall covering 1,000 miles is estimated to cost $20 billion.

The wall was one of President Trump's signature campaign promises, and he swore Mexico would eventually pay for the wall. Trump asked for $2.6 billion for the wall in his federal budget blueprint last month. He's also asked for an additional $1.5 billion in a supplemental spending measure for fiscal 2017.

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Existing fence along America’s southern border costs about $2.8 million per mile, according to ProPublica, which says about 650 miles of the 2,000-mile-long border already has some form of fencing.

CBP reportedly plans on spending its existing funds on eight model walls, planning, engineering and early-stage land acquisition.

Mark Borkowski, CBP's chief procurement officer, said construction on the wall will start at least two years after that if full funding is provided by Congress.

GOP leaders likely won't attach wall funding to April's government spending bill, leaving the question of when Republicans will push for wall funding unclear.