IMF chief economist Pierre-Olivier Gourinchas, in his parting interview before leaving next week, warned that "tit-for-tat" trade warfare is "self-defeating." The timing was deliberate — he spoke hours after Donald Trump threatened a 100% tariff on any country that taxes American tech giants. The trade war isn't broadening; it's mutating into a new dimension.

Trade Routes

• United States: Trump declared on Truth Social that any nation imposing a Digital...