We’ve heard a lot about democratic socialism lately, as the self-described socialist Sen. Bernie Sanders poses an ever-bigger threat to Hillary Clinton. But what is democratic socialism?

Wikipedia defines it as “a political ideology advocating a democratic political system alongside a socialist economic system, involving a combination of political democracy with social ownership of the means of production.” The Democratic Socialists of America explain that “democratic socialists believe that both the economy and society should be run democratically.” That doesn’t sound so bad — running things “democratically.” But what it means is that the government would run the entire economy and society, and all decisions would be made by the political process.

Now, Sanders dances around just how far his own socialism goes. At a recent speech he said,“I don’t believe government should own the grocery store down the street or control the means of production, but I do believe that the middle class and the working families who produce the wealth of America deserve a fair deal.” But he has spoken at numerous DSA events, and in the past he has written about putting television under “democratic control.”

I doubt that the 26 percent of young people who tell pollsters that they have a favorable view of socialism actually want television put under the direct control of politicians. But be careful what you wish for.

Robert Heilbroner, perhaps the best-selling socialist writer of the 20th century, was more honest than many socialists. He wrote in Dissent magazine:

Socialism…must depend for its economic direction on some form of planning, and for its culture on some form of commitment to the idea of a morally conscious collectivity.…

If tradition cannot, and the market system should not, underpin the socialist order, we are left with some form of command as the necessary means for securing its continuance and adaptation. Indeed, that is what planning means…

The factories and stores and farms and shops of a socialist socioeconomic formation must be coordinated…and this coordination must entail obedience to a central plan…

The rights of individuals to their Millian liberties [are] directly opposed to the basic social commitment to a deliberately embraced collective moral goal… Under socialism, every dissenting voice raises a threat similar to that raised under a democracy by those who preach antidemocracy.

Not only does a socialist economy require a central plan, he said, but a plan will require us to subordinate our personal liberties — liberties of choice and free speech, associated with John Stuart Mill — to the plan of the government. That hardly seems like a future today’s millennials — or any other American — would want to live in.

By the way, Dissent republished this article this past November under the heading “What Is Democratic Socialism?”

Heilbroner also noted that “democratic liberties have not yet appeared, except fleetingly, in any nation that has declared itself to be fundamentally anticapitalist.”

Heilbroner understood socialism. Sanders is evasive about just what he means by socialism. And recently, both Hillary Clinton and Democratic national chair Debbie Wasserman Schultz refused to answer the question, “What’s the difference between a Democrat and a socialist?”

Real socialism has been a disaster in countries from the Soviet Union to Tanzania. Attempts to move sharply toward socialism have produced results such as today’s Venezuela, with shortages of toilet paper and soap. And even the European countries that Bernie Sanders praises, such as Sweden and France, have higher unemployment rates and lower overall incomes than the somewhat more capitalist United States.

Voters should take note of socialism’s failures and of Heilbroner’s warning about what socialism requires. And they should be very skeptical of any candidate who speaks warmly of socialism or can’t explain how his or her own political views differ from socialism.