Nearly two years after the Brexit referendum, the U.K. stands on the brink of a full-blown political crisis.
Until now, Prime Minister Theresa May has been able to hold a divided government, party and country together by ducking hard choices or denying that hard choices need to be faced. Although she voted to remain, she embraced the Brexiter fantasy that quitting the European Union would be easy: that the U.K. could halt payments to Brussels, stop EU citizens from coming to work in Britain, ditch EU single-market rules and...