The head of the European Central Bank warned that global friction over trade — such as U.S. threats to impose more tariffs — is holding back the economy as he underlined the bank’s readiness to deploy more stimulus if needed. Mario Draghi said Wednesday that an improving jobs market and rising wages were helping the economy in the 19 countries that use the euro but uncertainties like trade disputes and Brexit are hurting it. “Global headwinds continue to weigh on euro area growth,” he told a news conference after the central bank kept its key interest rates and policy promises...