LONDON—Boris Johnson, the ebullient Brexiteer who has promised to lead Britain out of the European Union with or without a deal by Halloween, will replace Theresa May as prime minister after winning the leadership of the Conservative Party on Tuesday, July 23.
His victory catapults the United Kingdom towards a Brexit showdown with the EU and towards a constitutional crisis at home, as British lawmakers have vowed to bring down any government that tries to leave the bloc without a divorce deal.
