It is done at last. As of Jan. 1, with the Brexit transition period over, Britain is no longer part of the European Union¡¯s single market and customs union. The departure was ordered, thanks to a last-minute deal running to more than 1,200 pages, but still painful to both sides. A great loss will be consummated.

Loss for the European Union of one of its biggest member states ¡ª a major economy, a robust military and the tradition, albeit faltering, of British liberalism at a time when Hungary and Poland have veered toward nationalism.

Loss for Britain of diplomatic heft in a world of renewed great power rivalry; of some future economic growth; of clarity over European access for its big financial services industry; and of countless opportunities to study, live, work and dream across the continent.