Politics is in a plastic period. And so is the Left. In Britain, what once seemed unthinkable has happened. The Labour left have steadily taken control of their party. The whole history of the Labour Party seems to militate against this, as even sympathizers, like the late Ralph Miliband, have long pointed out. And after two decades in which the apostles of Tony Blair’s New Labour had exercised tight control and sought to remold the party in their own image, the prospects for the Labour left seemed less propitious than ever. And yet, their candidate, Jeremy Corbyn, first won the Labour leadership in 2015, saw off a unprecedented leadership challenge from his own MPs in 2016, and followed that by significantly increasing Labour share of the vote from 30 percent to 40 percent in the snap general election of 2017, leaving the governing Conservative Party without a majority in its own right. His supporters now control Labour’s National Executive.

Is this simply a singular development — a British one-off? Or is it part of a more general shift in politics that we might also expect to see elsewhere? Let me start by comparing the British case with the United States. I’ll then turn to other English-speaking countries, before finally comparing the British case with the most recent developments in the established democracies of continental Europe.

Prima facie, the United States seems to have experienced similar developments, with the rise of Bernie Sanders. Like Corbyn, Sanders was an insurgent candidate from outside the party establishment, with a long record of dissident integrity, and the reputation for authenticity which that fostered. And like Corbyn, he held views that were seen as well to the left of either the median voter or parliamentarian, and had until recently been thought of as a marginal figure in the political firmament. Indeed if anything, all of this was more true of Sanders than of Corbyn. In Britain, a notionally socialist party had long been a contender for government. In the United States, socialism was widely seen in both scholarly studies and public debate as beyond the bounds of mainstream politics. And the idea that a candidate might get anywhere near national office while embracing the label of socialism has seemed well-nigh inconceivable for over a century. The best result socialist activists could point to was Eugene Debs’s 6 percent in 1912. And yet here was Sanders: a figure who came close to becoming a major party presidential candidate and who, opinion polls showed, had he become the candidate, may well have won the presidential election itself.