European leaders are bracing for U.S. tariffs after President Donald Trump imposed sweeping levies on Mexico, Canada and China that will affect billions of dollars' worth of trade. On Monday, Trump agreed to a one month pause on tariffs planned for Mexico as negotiations continue. He also threatened steeper tariffs elsewhere, telling reporters it will “definitely happen” with the European Union. The U.S. president said Americans could feel “some pain,” but it will “worth the price” to enhance U.S. interests. We speak with Joel Paul, professor of constitutional law, international business and trade, foreign relations and national security law at UC Law San Francisco.