A political novice who calls herself a “democratic socialist” wins an unexpected Democratic Party primary victory, and now political taxonomists are racing to explain just what the term means. Here’s my definition: political hemlock for the Democratic Party.

I write, of course, of Alexandria Ocasio-Cortez. She’s the onetime Bernie Sanders organizer whose victory last month over long-term New York congressman and party boss Joe Crowley is being compared to Tea Partyer Dave Brat’s 2014 primary defeat of the Republican House majority leader, Eric Cantor — a sign of what’s to come, both for the Democratic Party and the country at large.

Well, maybe. It wasn’t long ago — March — that Marine reservist and former federal prosecutor Conor Lamb was feted as the Democratic future for winning a House seat in a Pennsylvania district that Donald Trump had carried by 20 points. The shared secret of Lamb’s and Ocasio-Cortez’s success is that they ran energetic campaigns, reflected the values of the people they sought to represent, and faced lackluster or entitled opponents.

Not every political contest is a battle of ideas. Sometimes it’s just a matter of showing up.

Still, it should be said: “Democratic socialism” is awful as a slogan and catastrophic as a policy. And “social democracy” — a term that better fits the belief of more ordinary liberals who want, say, Medicare for all — is a politically dying force. Democrats who aren’t yet sick of all their losing should feel free to embrace them both.

Start with democratic socialism. The Democratic Socialists of America, of which Ocasio-Cortez is a member, believe in economies defined by state-owned enterprises and worker-owned cooperatives. Versions of this have been tried to varying degrees before: Israel in its first decades; post-independence India; Sweden in the 1960s and ’70s.

It always led to crisis: hyperinflation for Israel in 1980s; an I.M.F. bailout for India in 1991; a banking meltdown for Sweden in 1992. It’s usually a recipe for corruption: State-owned enterprises such as Pemex in Mexico or Eskom in South Africa are local bywords for graft and mismanagement. It frequently leads to dictatorship. Hugo Chávez was also a democratic socialist.

People used to know this stuff. That someone like Ocasio-Cortez apparently doesn’t is a fresh reminder that, in politics as in life, the most obvious lessons are the ones you can least afford to stop teaching.

What about social democracy? Isn’t it the norm in Europe, and isn’t it working pretty well? You wouldn’t know it by the way Europeans are voting. France’s Socialists ran a left-wing candidate in last year’s presidential election, and crawled away with barely 6 percent of the vote. Germany’s Social Democrats had their worst electoral result since 1933. Italy’s center-left was trounced by a combination of populists and right-wingers in March.

You can argue that the major goals of social democracy — universal health care and other social provisions — were achieved long ago in Europe. But they aren’t so fully realized, and are thus potentially popular, in America, never mind our own robust welfare state.

But that misses the deeper point. Today’s social democracy falls apart on the contradiction between advocating nearly unlimited government largess and nearly unlimited immigration. “Abolish ICE” is a proper rallying cry for hard-core libertarians and Davos globalists, not democratic socialists or social democrats. A federal job guarantee is an intriguing idea — assuming the jobs are for some defined “us” that doesn’t include every immigrant, asylum-seeker or undocumented worker.

Trump gets this, as does the far right in Europe, which is why they attract such powerful working-class support. Want to preserve the welfare state? Build a wall — or, in Europe’s case, reinstate border controls. Want more immigrants and amnesty? Lower the minimum wage and abolish the closed shop.

But please choose. It’s one or the other.

It’s possible Democrats will surrender to the illusion that they can have both, puffing the sails of Ocasio-Cortez and her fellow travelers. But a Democratic Party seriously interested in defeating congressional Republicans in the fall and Trump in 2020 isn’t going to win by turning itself into a right-wing caricature of the left, complete with a smug embrace of whatever it conceives to be “socialism.”

If Trump is the new Nixon, the right way to oppose him isn’t to summon the ghost of George McGovern. Try some version of Bill Clinton (minus the grossness) for a change: working-class affect, middle-class politics, upper-class aspirations.

I’ve written elsewhere that a chief danger to democracy is a politics in which the center bends toward the fringe instead of the fringe bending toward the center. It’s the way Trump became president. But the antidote to one extreme isn’t another, and Democrats will only win once they reclaim the vital center of American politics.

The center is Dayton and Denver, not Berkeley and Burlington. The center is Harry Truman and Daniel Patrick Moynihan, not Eugene Debs and Michael Harrington. Democrats who want to win should know this. ☐