Now that Zohran Mamdani has won the New York City mayoral primary, the New York Times is asking the question, “Zohran Mamdani Says He’s a Democratic Socialist. What Does That Mean?” The article doesn’t provide much of an answer. Instead, it trots out my old bête noire, Sheri Berman, who offers up crisp nuggets of wisdom like this: “These labels are fuzzy.”

If only the Times editors read their own paper. In the wake of the Bernie campaign and AOC’s election, the Times asked me to write a piece explaining the meaning of democratic socialism for a new generation. Since I think the piece holds up, and helps us understand some of the particular appeal of the Mamdani campaign—his focus on free public goods, his focus on the local, his embrace of immigrants and his own international story, his insistence on democratic action—I’m reproducing it here.

Long story short: the key to socialism is freedom.

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Throughout most of American history, the idea of socialism has been a hopeless, often vaguely defined dream. So distant were its prospects at midcentury that the best definition Irving Howe and Lewis Coser, editors of the socialist periodical Dissent, could come up with in 1954 was this: “Socialism is the name of our desire.”

That may be changing. Public support for socialism is growing. Self-identified socialists like Bernie Sanders, Alexandria Ocasio-Cortez and Rashida Tlaib are making inroads into the Democratic Party, which the political analyst Kevin Phillips once called the “second-most enthusiastic capitalist party” in the world. Membership in the Democratic Socialists of America, the largest socialist organization in the country, is skyrocketing, especially among young people.

What explains this irruption? And what do we mean, in 2018, when we talk about “socialism”?

Some part of the story is pure accident. In 2016, Mr. Sanders made a strong bid for the Democratic presidential nomination. Far from hurting his candidacy, the “socialism” label helped it. Mr. Sanders wasn’t a liberal, a progressive or even a Democrat. He was untainted by all the words and ways of politics as usual. Ironically, the fact that socialism was so long in exile now shields it from the toxic familiarities of American politics.

Another part of the story is less accidental. Since the 1970s, American liberals have taken a right turn on the economy. They used to champion workers and unions, high taxes, redistribution, regulation and public services. Now they lionize billionaires like Bill Gates and Mark Zuckerberg, deregulate wherever possible, steer clear of unions except at election time and at least until recently, fight over how much to cut most people’s taxes.

Liberals, of course, argue that they are merely using market-friendly tools like tax cuts and deregulation to achieve things like equitable growth, expanded health care and social justice — the same ends they always have pursued. For decades, left-leaning voters have gone along with that answer, even if they didn’t like the results, for lack of an alternative.

It took Mr. Sanders to convince them that if tax credits and insurance exchanges are the best liberals have to offer to men and women struggling to make stagnating wages pay for bills that skyrocket and debt that never dissipates, maybe socialism is worth a try.

Socialism means different things to different people. For some, it conjures the Soviet Union and the gulag; for others, Scandinavia and guaranteed income. But neither is the true vision of socialism. What the socialist seeks is freedom.

Under capitalism, we’re forced to enter the market just to live. The libertarian sees the market as synonymous with freedom. But socialists hear “the market” and think of the anxious parent, desperate not to offend the insurance representative on the phone, lest he decree that the policy she paid for doesn’t cover her child’s appendectomy. Under capitalism, we’re forced to submit to the boss. Terrified of getting on his bad side, we bow and scrape, flatter and flirt, or worse — just to get that raise or make sure we don’t get fired.

The socialist argument against capitalism isn’t that it makes us poor. It’s that it makes us unfree. When my well-being depends upon your whim, when the basic needs of life compel submission to the market and subjugation at work, we live not in freedom but in domination. Socialists want to end that domination: to establish freedom from rule by the boss, from the need to smile for the sake of a sale, from the obligation to sell for the sake of survival.

Listen to today’s socialists, and you’ll hear less the language of poverty than of power. Mr. Sanders invokes the 1 percent. Ms. Ocasio-Cortez speaks to and for the “working class” — not “working people” or “working families,” homey phrases meant to soften and soothe. The 1 percent and the working class are not economic descriptors. They’re political accusations. They split society in two, declaring one side the illegitimate ruler of the other; one side the taker of the other’s freedom, power and promise.

Walk the streets of Bushwick with a canvasser for Julia Salazar, the socialist candidate running to represent North Brooklyn in the New York State Senate. What you’ll hear is that unlike her opponent, Ms. Salazar doesn’t take money from real estate developers. It’s not just that she wants to declare her independence from rich donors. It’s that in her district of cash-strapped renters, landlords are the enemy.

Compare that position to the pitch that Shomik Dutta, a Democratic Party fund-raiser, gave to the Obama campaign in 2008: “The Clinton network is going to take all the establishment” donors. What the campaign needed was someone who understands “the less established donors, the real-estate-developer folks.” If that was “yes, we can,” the socialist answer is “no, we won’t.”

One of the reasons candidates like Ms. Ocasio-Cortez and Ms. Salazar speak the language of class so fluently is that it’s central to their identities. Al Gore, John Kerry and Hillary Clinton struggled to cobble together a credible self out of the many selves they’d presented over the years, trying to find a personal story to fit the political moment. Today’s young candidates of the left tell a story of personal struggle that meshes with their political vision. Mr. Obama did that — but where his story reinforced a myth of national identity and inclusion, the socialists’ story is one of capitalism and exclusion: how, as millennials struggling with low wages and high rents and looming debt, they and their generation are denied the promise of freedom.

The stories of these candidates are socialist for another reason: They break with the nation-state. The geographic references of Ms. Ocasio-Cortez — or Ms. Tlaib, who is running to represent Michigan’s 13th District in Congress — are local rather than national, invoking the memory and outposts of American and European colonialism rather than the promise of the American dream.

Ms. Tlaib speaks of her Palestinian heritage and the cause of Palestine by way of the African-American struggle for civil rights in Detroit, while Ms. Ocasio-Cortez draws circuits of debt linking Puerto Rico, where her mother was born, and the Bronx, where she lives. Mr. Obama’s story also had its Hawaiian (as well as Indonesian and Kenyan) chapters. But where his ended on a note of incorporation, the cosmopolitan wanderer coming home to America, Ms. Tlaib and Ms. Ocasio-Cortez aren’t interested in that resolution. That refusal is also part of the socialist heritage.

Arguably the biggest boundary today’s socialists are willing to cross is the two-party system. In their campaigns, the message is clear: It’s not enough to criticize Donald Trump or the Republicans; the Democrats are also complicit in the rot of American life. And here the socialism of our moment meets up with the deepest currents of the American past.

Like the great transformative presidents, today’s socialist candidates reach beyond the parties to target a malignant social form: for Abraham Lincoln, it was the slavocracy; for Franklin Roosevelt, it was the economic royalists. The great realigners understood that any transformation of society requires a confrontation not just with the opposition but also with the political economy that underpins both parties. That’s why realigners so often opt for a language that neither party speaks. For Lincoln in the 1850s, confronting the Whigs and the Democrats, that language was free labor. For leftists in the 2010s, confronting the Republicans and the Democrats, it’s socialism.

To critics in the mainstream and further to the left, that language can seem slippery. With their talk of Medicare for All or increasing the minimum wage, these socialist candidates sound like New Deal or Great Society liberals. There’s not much discussion, yet, of classic socialist tenets like worker control or collective ownership of the means of production.

And of course, there’s overlap between what liberals and socialists call for. But even if liberals come to support single-payer health care, free college, more unions and higher wages, the divide between the two will remain. For liberals, these are policies to alleviate economic misery. For socialists, these are measures of emancipation, liberating men and women from the tyranny of the market and autocracy at work. Back in the 1930s, it was said that liberalism was freedom plus groceries. The socialist, by contrast, believes that making things free makes people free.

It’s also important to remember that the traffic between socialism and liberalism has always been wide. The 10-point program of Marx and Engels’s “Communist Manifesto” included demands that are now boilerplate: universal public education, abolition of child labor and a progressive income tax. It can take a lot of socialists to get a little liberalism: It was socialists in Europe, after all, who won the right to vote, freedom of speech and parliamentary democracy. Given how timid and tepid American liberalism has become — when was the last time a Democratic president even called himself a liberal — it’s not surprising that a more arresting term helps get the conversation going. Sometimes nudges need a nudge.

Still, today’s socialism is just getting started. It took Lincoln a decade — plus a civil war, and the decision of black slaves to defy their masters, rushing to join advancing Union troops — to come to the position that free labor meant immediate abolition.

In magazines and on websites, in reading groups and party chapters, socialists are debating the next steps: state ownership of certain industries, worker councils and economic cooperatives, sovereign wealth funds. Once upon a time, such conversations were the subject of academic satire and science fiction. Now they’re getting out the vote and driving campaigns. It’s too soon to tell whether they’ll spill over into Congress, but events have a way of converting barroom chatter into legislative debate.

What ultimately gives shape to socialist desire is less the specific policies in a politician’s head than the men and women marching with their feet. That’s why the two most important utterances of today’s socialists are Ms. Salazar’s demand that New York abolish the law prohibiting strikes of government workers and Ms. Ocasio-Cortez’s call “to occupy all of it.” Both statements reveal what socialists have always understood: Mass action — sometimes illegal, always confrontational — will determine socialism’s final form.

Socialism is not journalists, intellectuals or politicians armed with a policy agenda. As Marx and Engels understood — this was one of their core insights, what distinguished them from other socialist thinkers, ever ready with their blueprints — it is workers who get us there, who decide what and where “there” is.

That, too, is a kind of freedom. Socialist freedom.