On Saturday, in Long Island City, N.Y., rising star Rep. Alexandria Ocasio-Cortez (D-N.Y.) endorsed Sen. Bernie Sanders (I-Vt.) before a massive crowd of more than 25,000 supporters. Just a few weeks ago, many observers were writing the Vermont senator off after he was sidelined by a heart attack. But with Ocasio-Cortez’s endorsement, as well as that of Rep. Ilhan Omar (D-Minn.) and his widely praised performance at Tuesday’s Democratic debate, the Vermont senator was well-justified in telling his cheering supporters, “I am back.”

As Ocasio-Cortez said in her video endorsing Sanders, “This is not just about running for president. This is about creating a mass movement.” The real significance of Ocasio-Cortez and Omar’s endorsements isn’t that they boosted Sanders’s campaign, but that they have gained enough influence that their endorsements can be the centerpiece of a campaign comeback rally. The movement has crossed a key threshold: For the first time in decades, the American left has a powerful presence in electoral politics.

Believe it or not, there was a time when democratic socialists were active in shaping the American political agenda. Labor leaders such as A. Philip Randolph and activists such as Bayard Rustin played major roles in the civil rights movement, with Randolph among the leaders who pressured President Harry Truman to desegregate the military. In the early 1960s, democratic socialist leader Michael Harrington’s book “The Other America” caught the attention of President John F. Kennedy. At the White House’s invitation, Harrington would continue to contribute anti-poverty proposals, a role he continued through the Lyndon B. Johnson administration.

During the 1970s, Harrington and others continued to be players in Democratic Party politics, particularly in the 1980 primary fight between President Jimmy Carter and Sen. Ted Kennedy. But in the wake of Ronald Reagan’s 1980 victory, many Democratic leaders became scared to be seen even as liberal, let alone leftist. Jesse Jackson’s “Rainbow Coalition” campaign in 1988 was the last great leftist hurrah in national politics for years.

Then came a quarter-century essentially in the wilderness. There were rare exceptions, including Sanders himself and Rep. Ron Dellums (Calif.), who in 1970 became the first socialist elected to Congress since Rep. Victor L. Berger left the House in 1929. But for the most part, leftist politicians and their policy ideas were excluded from influence in American politics — not that their absence stopped Republicans labeling anything Democrats put forward as socialist.

The Great Recession and years of rising inequality finally changed that. Millions of voters, especially young voters, went looking for an alternative. For all his candidacy made that hunger clear, the “political revolution” Sanders calls for was never going to happen if its success or failure hinged entirely on whether he captured the White House. But now he has supporters such as Omar and especially Ocasio-Cortez who themselves have impressive followings and who can marshal serious voter power for the left’s causes.

So whatever happens to Sanders’s 2020 campaign, the movement behind it likely will continue to be a force to be reckoned with. Dozens of democratic socialists have been elected to federal, state and local offices across the U.S. Membership in the Democratic Socialists of America — cofounded by Harrington — has grown tenfold since 2015. Even Democratic National Committee Chairman Tom Perez has said Ocasio-Cortez “represents the future of our party.”

The evidence of this influence isn’t just tallied in election results. It’s obvious in the policy agenda that Democrats are debating on the campaign trail and in Congress, including Medicare-for-all, a remade tax system to massively reduce inequality, a Green New Deal to fight climate change and fix our broken infrastructure, and a complete reform of the criminal-justice system. As Ocasio-Cortez puts it, “This is about unconditional, universal, guaranteed advanced standard of living in the United States.”

“I share an immediate program with liberals in this country,” Harrington once said, “because the best liberalism leads toward socialism. I’m a radical, but as I tell my students at Queens, I try not to soapbox. I want to be on the left wing of the possible.” For years after his death, though, the “left wing” of American politics was markedly to the right of any democratic socialist program. Finally, in Sanders, Ocasio-Cortez, Omar and other officeholders around the country, there is once again an electorally powerful American left that will endure beyond one politician or one election. That’s not just good for the Democratic Party; it’s good for the country.

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