In Search for Leverage, Trump May Be Undercutting His Own Trade Deals

President Trump is embracing a new tactic as he tries to rewrite the rules of global trade: Don’t believe a final deal is truly final.

Mr. Trump, who has called deal-making his “art form,” has used his unpredictability as a source of leverage in discussions with Europe, Canada, Mexico, Japan and elsewhere. He has dangled the possibility of lifting American metal tariffs while threatening to add new tariffs on automobiles at any time. He has repeatedly agreed to new trade terms with foreign partners, then talked about undoing those deals...