After the Labour Party’s electoral defeat in Britain last year, the party’s small left caucus debated whether it should stand a candidate for the leadership at all. Some feared defeat would expose just how small the caucus was. Others insisted that someone needed to at least raise the arguments against anti-austerity and for a progressive foreign policy to counter the narrative that Labour had lost because it was too progressive.

Once the caucus resolved in favor of standing a candidate, the next challenge was to find a candidate. There were few takers. “What about if I stand?” asked Jeremy Corbyn, a consistent socialist standard-bearer over several decades. The question was initially met with silence. But when nobody else came forward, Corbyn got the nod. Then came the final task: getting on the ballot. For that, Corbyn needed 35 members of Parliament to nominate him. With just hours to go before the deadline, he was still several signatures short. With seconds left, his supporters rounded up some parliamentarians who didn’t support him but voted for him anyway, just so the party could have the fullest debate possible.

Nobody—least of all Corbyn—assumed that he would win the debate, let alone the election, with one of the largest majorities of any Labour leader.

The trajectory of Corbyn’s ascent—the unlikeliness, pace, and impact of it; the breadth, depth, scale, and insurrectionary nature of it—is emblematic of a broader and growing trend in much of the Western world. In different ways, and to different extents, it is reflected in Bernie Sanders’s campaign for the Democratic nomination, as well as the rise of Podemos in Spain, the Left Bloc in Portugal, and Syriza in Greece. (The fact that Sanders is all but certain to lose is irrelevant. What is remarkable is that he ever had a chance, no matter how slim.)

All of these political movements are, of course, different in their own way. Some, like Podemos and Syriza, are relatively new formations, expressing the hope for a different kind of political engagement. Others—the challenges by Sanders and Corbyn in particular—are fronted by older men within established institutions and blend nostalgia for an abandoned social-democratic agenda with the youthful energy of a generation that speaks the language of class almost as fluently as it does that of identity. Some are the product of movements that have grown out of the most recent crisis; others are trying to create movements in order to sustain them.

But all have this in common: They have created electoral space on the left where few believed it was possible to thrive, let alone win. In so doing, they have surprised both themselves and their moderate opponents, upending the political certainties of a generation. This new situation poses challenges for everyone.

For a generation, the liberal establishment claimed that radical agendas were self-indulgent precisely because they could not win. “We want to change people’s lives,” went the mantra of Tony Blair, Bill Clinton, and any number of social democrats in between. “But we can’t do that if we’re not in power, and we can’t gain power with a radical agenda.” This, of course, became a self-fulfilling prophecy: No one will vote for those radical policies, so we won’t offer them; since they weren’t offered, no one could vote for them. Pretty much everything could be justified on the basis that the other lot were much worse.

This logic no longer holds. In any number of theoretical general-election matchups, Sanders has outshined Hillary Clinton against both Donald Trump and Ted Cruz, with double her national lead in the polls. Though Sanders fares worse against John Kasich, this admittedly crude yardstick still suggests he’d win in November.

In the United Kingdom, despite hostile media, a parliamentary party in revolt, and considerable self-inflicted wounds, Corbyn has, in the last couple of months, started to lead in the occasional opinion poll. Syriza won reelection in Greece; the Left Bloc is propping up the social-democratic government in Portugal; Podemos is now a serious force in Spain that could, if it joins forces with another radical party (United Left), eclipse the long-established Spanish Socialist Workers’ Party.

This electoral revival on the left is impressive, but hardly decisive. None of this makes victory likely, let alone inevitable in most cases. But it does make these candidacies viable and their agendas quite evidently plausible. It belies the claim “Vote for Bernie and you’ll get Trump.” That line of reasoning was always more of a threat than an argument. But it doesn’t work even as a threat now. The facts simply don’t support it; informed conjecture can no longer sustain it.

So the establishment has to own its politics. If it wants to balance budgets on the backs of the poor or deregulate industries to fill the pockets of the rich, it will have to make its case. If, ultimately, it doesn’t seek a society that is fair but one that is merely a bit less unfair, then it should say so rather than hide behind the ostensible will of an electorate that has been offered no other choice. If what masqueraded as pragmatism was really principle in drag, then it deserves to be outed.

But, similarly, it falls on the radical left to take itself far more seriously. When it comes to elections, it can no longer act like the dog that chases a car only to end up confounded when it actually catches the vehicle. True, there’s more to politics than elections and more to elections than just winning. But the days of standing for office in order to shift the debate, broaden the base, or just make a point may be over. The debate has shifted; the base has been broadened; the point has been made unmistakably.

Radicals now have to take yes for an answer and decide how to employ the electoral strength they’ve marshaled. Having cleared political space through the ballot box, the left must now decide how to build on it.