The European Union says it will respond to any imposition of tariffs by the U.S. – sparking concerns that the two sides could be heading towards a trade war. Washington has vowed to impose a 25% duty on all aluminum and steel imports and match tariffs that other nations currently have in place. The U.S. and EU have the largest bilateral trade relationship in the world and officials are warning of economic pain on both sides of the Atlantic. William Denselow reports from Brussels.