U.S. President Donald Trump is headed for a showdown with America's allies at a Group of Seven summit this week in Quebec, with the European Union and Canada threatening retaliatory measures unless he reverses course on new steel and aluminum levies.

China, meanwhile, is warning it will withdraw commitments it made on trade if the president carries out a separate threat to impose tariffs on Asia's top economy. While China doesn't want an escalation in trade tensions, it has the confidence, competence and experience to defend its core interests, according to a commentary published Monday by state-run Economic Daily.

Trump changes his mind often enough that U.S. allies and rivals alike hope he'll do just that on tariffs in the next few days. An all-out trade war may become unavoidable if he doesn't.