The problem seemed to separate the president from prominent republicans. He drew his condemnation not only from the establishment wing of his party, including the powerful Senator Orrin Hatch, but also from anti-establishment conservatives such as Mark Meadows, who led the right caucus on Capitol Hill.
Meadows tweette: & # 39; & # 39; Rates on steel and aluminum are a tax increase that the American people do not need and can not pay. & # 39; & # 39;
Trump has received several requests to save Canada.
The Pentagon even published a letter in which he was urged not to aim at allies. During witness statements, witness witnessed to the government a special exemption for Canada, given the joint car sector, the shared aluminum market and the integrated defense industrial complex served by the metals.
Even the trade unions that support the rates have lobbied for a Canadian exemption. That includes the well-connected United Steelworkers trade union, which has members in both countries, and a president from Canada, Leo Gerard.
Gerard has urged the administration to leave his home and country of birth.  "Putting Canada in the same boat as Mexico, or China, or India, or South Korea … is not right," he said in an interview.
"Canada just has to be excluded – period, we have an integrated economy and if it is undone, America will pay a high price … In every opportunity I've had, I've tried to point out the main decision makers that Canada is not the problem when it comes to international trade – and to do something that would lead to the disregard of Canada (the US). "
Last year Canada exported approximately C $ 9.3 billion in aluminum and C $ 5.5 billion of steel to the US, where Canadian steel represented just over 15 percent of total imports. Nearly ninety percent of Canadian exports even went straight to the south.
But the problem is significant far beyond North America.
Several trade experts have warned that such free use of an exemption from national security invites others to do the same and could lead to a domino effect of reprisals. Mexico and Europe are already threatening with counter-rates.
"Trump's national security policy opens the Pandora's box," exclaimed a piece by Forbes from trade analyst Dan Ikenson.
Edward Alden of the American Council for External Relations, on Twitter, added: "This is the US's most consistent protectionist action since (Richard) Nixon's 10 percent across-the-board tariffs in 1971. And those did not last very long. "
The Canadian government and its business allies are planning to continue lobbying for an exemption. In Washington, some hoped that Trump would get cold feet – as he has done before with specific policies, such as immigration reforms.
However, bringing Americans to the attention can be a challenge.
Word of the tariffs was partially lost Thursday in an avalanche of American political news. The news network MSNBC showed a graph that illustrated all the big stories it was trying to keep track of – from the Russian probe to alleged conflicts of interest in the White House; from rifle legislation to ongoing power struggles within the administration.
It said: "48 hours, 18 stories."
By Alexander Panetta, The Canadian Press