Mr. Lighthizer, the United States trade representative, voiced concern about the impact on ratifying the newly negotiated pact, known as the United States-Mexico-Canada Agreement, but he ultimately viewed his role as carrying out Mr. Trump’s decision.
Mr. Mnuchin privately believed the tariffs could derail the pact, complicate Washington’s rocky trade negotiations with China and risk unsettling stock markets, but in the end his objections were mostly about timing. Larry Kudlow, a noted free trader who leads the National Economic Council, was undergoing surgery for a hip replacement and was not present for key discussions.
“Ambassador Lighthizer never argued against the president’s tariff plan and agrees that this strong action is needed to resolve the longstanding, serious immigration crisis,” said a spokesman for the United States trade representative.
A Treasury spokesman declined to comment.
The president’s decision to impose the tariffs sent aides scrambling. On Thursday morning during a trip to Guatemala, Kevin K. McAleenan, the acting secretary for the Department of Homeland Security, was briefed on the White House’s coming announcement, causing him to be about 40 minutes late to a breakfast hosted by the United States ambassador to the country.
As Mr. McAleenan ate, top aides in the department called White House officials to learn more about the plan and to find out if it was actually a done deal. Around 2 p.m., top officials in the agency were still unclear if the president would follow through.
Inside the White House, Mr. Trump’s advisers tried to at least buy more time to try to secure a commitment from Mexico. At a meeting on Thursday, Mr. Mnuchin and other advisers persuaded the president to wait until June 10 before imposing the tariffs, in hopes that they could get Mexico to do something before then.
Mr. Trump agreed. On Thursday evening, he announced on Twitter that he would use emergency powers to impose a 5 percent tariff on June 10 and said that amount would increase to as much as 25 percent “until the Illegal Immigration problem is remedied.”