While Mattis said he was against countries "intentionally" using "unfair" trade practices to harm the USA defense industrial base - as opposed to outcompeting us, which is what some of the trading partners potentially affected by the Trump tariffs are actually doing - he also pointed out that USA industry can easily meet the military's steel and aluminum needs without protection.
The affected metals rose sharply, as the 10 percent tariff on aluminum and 25 percent tax on imported steel will increase the cost of foreign commodities, while domestic producers will likely raise their own prices to increase profits.
The biggest political challenge for Bush was the fury of the steel-consuming companies that were confronted with price hikes. The U.S. hasn't yet indicated if any countries will be excluded.
The American International Automobile Dealers Association warned it would drive up prices "substantially". Those manufacturers produce hundreds of thousands of cars in the United States each year, many of which are later exported to buyers in Asia and Europe. In the United States, the S&P 500 dropped as much as 1.1 percent before paring its decline.
European Union officials said they would retaliate with new tariffs on US goods, including Harley-Davidson motorbikes, bourbon whiskey and Levi's jeans.
WTO Director-General Roberto Azevedo said in a statement that a trade war would be in no one's interest. The real intention appears to be that curbing steel imports will revive the flagging United States steel industry and rejuvenate jobs. Trump has also said these sorts of threats could incentivize foreign companies to expand their US operations so they don't have to pay the import fees.
Mr Trump has a history of criticising European Union trade policy and in January of this year he said had "a lot of problems" with how the trade bloc behaves.
But the rhetoric ramped up as Mr Trump tweeted, "Trade wars are good". This week, he summoned steel and aluminum executives to the White House and declared he would levy penalties of 25 percent on imported steel and 10 percent on aluminum imports.
The President also said the EU, which is comprised of 28 European countries, had "banded together in order to beat the United States in trade". He said the policy is "being written now" and will be signed next week. "What benefits one industry can hurt another".
The prime minister of Canada - which exports more steel to the U.S. than any other country - slammed the tariffs as "absolutely unacceptable".
US Commerce Secretary Wilbur Ross downplayed the impact on autos, telling CNBC Friday that there's about a ton of steel in an average vehicle - and that commodity now costs $700.
Canada, the largest supplier of steel to the U.S., said tariffs would cause disruption on both sides of the border. He added that targeted tariffs would be preferable to global quotas or tariffs.
Trump's message on Saturday continued to levy direct attacks at US allies and some of the world's largest economies. Key Senate offices also did not receive advance notice. There are even members of the Republican Party who are opposed to the plan. But long time trends suggests that the picture is more complex.
"Trump is really shooting himself in the foot", Erixon said.
Trump's comments come as part of a wider focus on imported goods, including proposed tariffs on imported steel and aluminium. Foreign leaders, meanwhile, have responded swiftly, saying they will retaliate with tariffs of their own meant to inflict economic pain on US industries, some of which happen to be in politically sensitive parts of the country.
"We are not protectionist".
Global steel markets are fluid.