The news of Rep. Alexandria Ocasio-Cortez’s planned endorsement of Sen. Bernie Sanders came as a shock Tuesday night, capping his comeback performance at the fourth Democratic debate. Many expected she would not endorse at all, or at least not before the New York primary. AOC, some speculated, wouldn’t risk alienating mainstream Democrats who projected their own politics on a young, telegenic woman of color. They were wrong.

Even before his health scare, the pundit class had written off the Sanders campaign. Warren has recently overtaken Biden in most national polls, and the liberal commentariat has come to see her as both the front-runner and the Left’s standard-bearer. With four months to go before a single vote is cast, Sanders was written out of 2020 discussions.

Then came AOC joined by Ilhan Omar and Rashida Tlaib — at a moment that couldn’t have been more precarious. (We now know that, according to Politico, AOC informed Sanders of her decision to join his campaign as he lay in a hospital bed in Nevada recovering from a heart procedure.) Liberal pundits, already equating Warren’s professional-class reformism with Sanders’s working-class radicalism, would have been more than happy to keep promoting AOC, Omar, and Tlaib as political renegades against the status quo even if they had chosen to stay safely on the sidelines. The three representatives could have had the best of both worlds all without taking an enormous political risk. Instead, they took the risk.

But more than providing a great “comeback kid” media narrative, AOC’s endorsement is a testament to the vital importance of the Sanders campaign to the broader left project. After a half-century of political defeat and working-class collapse, it’s clear that we have a once-in-a-generation opportunity. A “good enough” progressive will not do for the severe challenges we face. A Sanders presidency is the only one among the current crop of candidates that could turn the tide.

The United States has had socialist labor leaders, mayors, congressional representatives, and countless activists and cultural denizens. But it has never had a socialist president — nor has it had an executive branch as powerful as the presidency is now in the twenty-first century. Due to many structural and historical strictures, the political configuration that launched socialists to power in nearly every major democracy in the world has so far eluded the United States. It’s not too much to suggest that a different path may be needed to begin a democratic-socialist reckoning here.

A US government helmed by a socialist president presents a unique opportunity for the Left — not because it would ensure democratic-socialist outcomes, but because it is an indispensable first step to rebuilding the political coalition and institutions that can deliver on the Left’s vision.

We have already seen the fruits of a socialist politician’s emergence at the national stage. Sanders’s 2016 run helped galvanize a nascent left movement and catalyze labor and political organizing. By their own accounts, Omar and AOC were inspired to launch their bid in large part by Bernie’s insurgent campaign for the Democratic nomination. Ocasio-Cortez’s unlikely rise as the face of the new Congress, despite Democrats’ victory coming out of flipping affluent suburbs, has shown the possibility of using the Democratic Party to pursue politics by and for the working class. What AOC’s still nascent political career — which began with her work on Sanders’s 2016 campaign — shows is the immense potential having a socialist at the top of the ticket can have in creating the next generation of socialist leaders.

Sanders has promised to be an “organizer-in-chief,” to support workplace democracy and employee ownership, to place Medicare for All and a Green New Deal at the top of his administration’s priorities. With the elections of AOC, Omar, and Rashida Tlaib — and now with them joining Sanders on the campaign trail to transform America — he and they are fighting to deliver on their promises. Something new is taking shape for the American left, a unique opportunity presented by his candidacy to build social democracy in America, rein in the long and destructive arm of American military policy, and unite a durable coalition that can build pro-worker policies for decades to come.

With Ocasio-Cortez’s endorsement of Sanders today and Omar’s and Tlaib’s earlier this week, the three of them have chosen not to take the politically easy path of laying low in the presidential race or endorsing a candidate who is far more palatable to the political establishment. Instead, they’ve thrown in their lots with the rising socialist movement in America and positioned themselves as electoral anchors for that movement in the years to come. And not a moment too soon.