In Executive Order 14193, President Donald J. Trump addresses the issue of illicit drugs entering the United States across its northern border with Canada. The order expands a national emergency previously declared for illegal immigration and drug trafficking, now including threats coming from Canada. To combat this, the President has announced the imposition of tariffs on Canadian goods, aiming to persuade Canada to take stronger actions against drug trafficking. If Canada retaliates with similar measures, the U.S. could increase or expand these tariffs.
Simple Explanation
President Trump made a rule to make Canada pay extra for selling things to the U.S. because he thinks Canada is not doing enough to stop bad drugs from coming into the U.S. from their side. If Canada gets upset and starts charging the U.S. more too, then the U.S. might charge even more in return, which could cause more problems between the two countries.