New tariffs on Canada, Mexico and China went into effect Tuesday as part of President Trump’s effort to use trade measures to halt the flow of fentanyl into America – and Canada has already retaliated.

Trump's threats to put tariffs on imports from Canada and Mexico have weighed on markets, even though there has been considerable uncertainty over whether he would make good on his threat.

Starting just past midnight, imports from Canada and Mexico are now to be taxed at 25 percent, with Canadian energy products getting tariffed at 10 percent.