Bloomberg reported that some Republican congressmen were driving behind the scenes efforts for tariff exemptions, including for farmers.

Ms Collins, the Maine Republican senator, said she had tried to persuade the White House to soften tariffs against Canada, which would affect the lobstering and paper mills industries in her home state. She told reporters that the decision to impose duties on it “just makes no sense.”

Meanwhile, Mr McConnell, the former Senate leader and long-time critic of the president, said tariffs on both Canada and Mexico would affect workers in his home state of Kentucky.

Other Republicans have been more supportive. Last week, Senator Jim Banks, an Indiana Republican, said the tariffs had led to Honda announcing plans to build a new hybrid vehicle in the state.