U.S. President Donald Trump's increased tariffs on steel and aluminum imports took effect on Wednesday as prior exemptions, duty free quotas and product exclusions expired, as his campaign to reorder global trade norms in favor of the U.

The move came after Ontario backed off imposing a surtax on U.S.-bound electricity, capping a rollercoaster day on Wall Street.

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.