Nigel Farage is the British crisis in human form. His party, the unambiguously named Brexit Party, which is hardly a party and didn’t exist six months ago, won nearly a third of the British vote in the recent European Parliament elections, putting it in first place and driving the shattered Conservative Party into fifth. Long underestimated, Mr. Farage has done more than any politician in a generation to yank British politics to the hard, nationalist right. He is one of the most effective and dangerous demagogues Britain has ever seen.

With his last political vehicle, the U.K. Independence Party, or UKIP, Mr. Farage took an assortment of Tory retirees and a smattering of ex-fascists and other right-wing cranks, and welded them into a devastating political weapon: a significant national party. That weapon tore such chunks out of the Conservatives’ share of the vote that the party leadership felt compelled to call a referendum on Europe — which it then lost. Mr. Farage declared victory and went into semiretirement as a pundit.