A 25 percent tariff on Canadian aluminum is an act of self-harm — economic self-mutilation — by the United States.

President Trump’s announcement on Monday that he was raising tariffs on all imports of steel and aluminum to 25 percent was all too familiar to Canadians, and to me, personally.

In 2018, when I was Canada’s foreign minister, the United States — our longtime friend, neighbor and military ally — imposed unjustified tariffs on Canadian steel and aluminum under a flimsy and frankly insulting national-security pretext.

Now, just four weeks into his second term, President Trump is once again upending the global trading order. First, he targeted America’s trade treaty partners Canada and Mexico with sweeping 25 percent tariffs, from which we have received a temporary reprieve. Days later, he imposed steel and aluminum tariffs on us and the rest of the world.

I saw this coming. As deputy prime minister and finance minister, I understood the threat posed by Mr. Trump’s aggressive economic nationalism. From the moment he was elected, I argued Canada needed to prepare for an emboldened Trump 2.0 who was intent on using trade as a weapon to sow chaos and scare capital and investment from all markets other than the United States.

Some Americans may feel this “might makes right” approach suits the current economic situation. The problem is that it will hurt America’s economy, too. Higher costs for supplies of steel and aluminum will hurt the very manufacturers and consumers President Trump claims to support.