Construction workers are seen next to heavy machinery while working on a new border wall in Santa Teresa, New Mexico, as seen from the Mexican side of the border in San Jeronimo, on the outskirts of Ciudad Juarez, Mexico April 23, 2018.

A White House effort to win support for a border wall describing the project as "border security" with "steel slats" only serves as a reminder that the president's steep tariffs on the metal would make any such project much more expensive.

So far this year, the price of milled steel products is up roughly 25 percent, which matches the level of import duties Trump applied in March to all steel products made outside the U.S. That added cost to imports helped domestic makers of steel and milled products raise their prices as well.

Despite congressional Democrats' opposition to Trump's demands of $5 billion for a border wall, the president Friday seemed determined to force a government shutdown. The move is aimed at showing his core supporters that he is steadfast in his commitment to his signature campaign promise to build a physical barrier between the U.S. and Mexico.

In a fumbled effort at compromise with Capitol Hill, the White House on Thursday tried to appease wall critics in Congress by describing the project differently.

Trump "does not want to go further without border security, which includes steel slats or a wall," White House spokeswoman Sanders told reporters.

It remains to be seen what materials would be used for a U.S.-Mexico border wall, let alone how much it would cost. Various estimates have placed the final cost of walling off the entire 2,000-mile boundary as high as $70 billion, according to a report by the Brookings Institution. It is unclear what the $5 billion the president is demanding would ultimately cover.

Cost estimates vary widely in part because the White House has yet to come up with final specifications. Even a concrete wall would get hit by tariffs, though, as steel would be used in that construction as well.

In August, the Government Accountability Office, a government watchdog agency, found that the Department of Homeland Security had not completed an analysis required to efficiently build the proposed barrier along the Mexico border — which could result in wasted taxpayer money.

"DHS plans to spend billions of dollars developing and deploying new barriers along the southwest border," the study said. "However, by proceeding without key information on cost, acquisition baselines, and the contributions of previous barrier and technology deployments, DHS faces an increased risk that the Border Wall System Program will cost more than projected, take longer than planned, or not fully perform as expected."

GAO did not estimate how much money could be wasted.