Free trade has been so beneficial to so many countries that the world may find a way to live without its biggest player.President Trump’s self-proclaimed “liberation day,” in which he announced across-the-board tariffs on the United States’ trading partners, carries an echo of another moment when an advanced Western economy threw up walls around itself.Like Brexit, Britain’s fateful vote nearly nine years ago to leave the European Union, Mr. Trump’s tariffs struck a hammer blow at the established order. He is pulling the United States out of the global economy much as Britain withdrew from a continentwide trading bloc, in...