WASHINGTON — If a trade war is coming, the cheesemakers of Wisconsin are standing in the line of fire. So are the farmers of the Great Plains and the distillers of Kentucky. And the employees of iconic American brands like Harley-Davidson and Levi Strauss. The likelihood of a trade conflagration leapt closer to reality this week after the United States imposed tariff on steel and aluminum imports from Canada, Mexico and the European Union.