President Trump has championed the U.S. steel industry, promising to strengthen it and to impose stiff tariffs on foreign metals to shield manufacturers from overseas competitors.

Yet the White House has secured tens of millions of dollars worth of donated foreign steel for Mr. Trump’s $400 million ballroom project, according to two people familiar with the plans who spoke on condition of anonymity to discuss sensitive and private conversations.

President Trump offered a surprising justification last month for forging ahead with construction of his White House ballroom: Halting the $400 million project would pose a grave threat to national security.

‘Everything is drone-proof and bulletproof,’ Mr. Trump said, listing the security features of a bunker being built beneath the ballroom to protect the president in the event of an emergency.

In December, after the administration took new steps to destroy the wind energy industry, with moves that even some of the president’s allies saw as radical, Interior Secretary Doug Burgum said the move was necessary “due to national security risks.”

Around the same time, Trump renewed his effort to annex Greenland and told reporters, “We need Greenland for national security.”

As part of a weird online harangue against the Times, the president justified his offensive by claiming that the newspaper is “a serious threat to the National Security of our Nation.”

The White House tried to defend its trade tariffs agenda in part by pointing to “national security” concerns.

When administration officials decided to ignore protections for endangered species and allow additional oil drilling in the Gulf of Mexico, they justified the move on national security grounds.

When the president targeted collective bargaining contracts for hundreds of thousands of federal employees, the White House defended the decision by saying their functions touch on national security.