President Donald Trump said Tuesday that he had ordered a doubling of the tariff on Canadian steel and aluminum, setting off a new wave of selling on Wall Street and raising fears that his insistence on overhauling the global trading system may involve significant costs.

President Donald Trump backed down from an extraordinary trade war escalation Tuesday that had threatened a massive surge in Canadian steel and aluminum tariffs and new tariffs on Canadian electricity.

Trump said he would increase from 25% to 50% tariffs taking effect Wednesday for Canada after Ontario said it would raise electricity prices on U.S.