President Donald Trump late Thursday threatened a 35% tariff on goods imported from Canada, a dramatic escalation in an on-again, off-again trade war with America’s northern neighbor and one of its most important trading partners.

The new tariff is an increase to the top 25% tariff rates that Trump first imposed in March after months of threats. Trump's tariffs were allegedly in an effort to get Canada to crack down on fentanyl smuggling despite the relatively modest trafficking in the drug from that country.