Democratic presidential candidate Sen. Bernie Sanders (I-Vt.) speaks at a rally in Los Angeles this month. (Lucy Nicholson/Reuters)

When Sen. Bernie Sanders came to speak in Iowa a few months ago, Drake University student Ian Miller snagged a seat on the stage. It was a close-up look at a historic campaign: After decades where socialists were the enemy, a “democratic socialist” had come to town as a serious candidate for president.

What a moment, right?

Right?

“Remind me what a socialist is?” Miller said last week.

A friend, Nik Wasson, tried to explain: “A socialist is someone who believes the government needs to be involved in a lot of aspects of the economy, and social issues as well.”

Senator Bernie Sanders (I-Vt.) has been making waves as the only democratic socialist running for president. Here’s what you need to know about being a democratic socialist and how it’s different from socialism. (Alice Li/The Washington Post)

“Okay,” said Miller, who was born in 1995. “Well, knowing what ‘democratic’ means — and now, knowing again what ‘socialist’ means,” he approved of the combination. “[Sanders] might want to see government have a heavier hand in certain policies,” he said, but “he wants everyone to have a say in it.”

Sanders’s remarkable success this year — in spite of his label as a socialist — is due to a mix of good politics and great timing.

Twenty-four years after the end of the Cold War, many Americans no longer associate socialism with fear or missiles — or with failure, food lines or empty Soviet supermarkets. A word that their elders saw as a slur had become a blank, open for Sanders to define.

And this year, Sanders (I-Vt.) has tried to define it with an eye toward a moderate audience.

He has called for huge growth in government regulation and spending. But he has stayed away from classic socialist ideas, like government takeovers of private industry. And, in his speeches, Sanders has talked about socialism in modest, solidly American terms: It’s nothing more than the pursuit of fairness in a country now rigged by the rich.

So far, it’s worked — but Sanders still hasn’t had to face an opponent determined to use socialism against him.

“What democratic socialism means to me,” Sanders said during a recent speech in New Hampshire, “is having a government which represents all people, rather than just the wealthiest people, which is most often the case right now in this country.”

Until recently, the word “socialist” occupied a special place in American politics: Along with “liar” and “hypocrite,” it was a rare insult so low-down that it couldn’t even be used on congressmen.

In 2011, for example, Alabama Rep. Mo Brooks (R) spoke the word on the House floor in 2011 — referring to Democrats as “socialist members.” There was a formal complaint, and Brooks retracted the word. In the Congressional Record, it was replaced by asterisks. “The *.*.* members of this body choose to spend money that we do not have,” Brooks said, officially.

Even now, socialists seem to be one of the most distrusted groups in American politics. In June, Gallup asked voters if they could vote for a socialist for president — if that socialist happened to be their own party’s nominee. Fifty percent said no. Gallup asked the same question about 10 other groups — Jews, Muslims, Mormons, evangelicals, gays, atheists and others — and socialists scored the worst.

Still, for Sanders, this has proven to be a ripe moment. One theory holds that President Obama may have helped pave the way.

“The public battle over Obama’s socialism has probably left a lot of his millennial supporters inclined to embrace the term on the theory that if Obama’s foes don’t like socialism, there must be something good about it,” said Stanley Kurtz, a conservative scholar whose book “Radical-in-Chief” argued that the president’s ideology had been informed by hard-left theorists.

Sanders doesn’t talk much about hard-left theories. He often tackles questions about socialism with a joke — which is only funny because times have actually changed.

“Does anyone here think I’m a strong adherent of the North Korean form of government? That I want all of you to be wearing similar-colored pajamas?” he says. The joke assumes that Sanders’s audiences no longer see old-style, Soviet socialism as a threat but as a weird foreign curiosity.

Indeed, some of them aren’t even that curious about it.

“Bernie is the one,” said Levi Vivanh, a freshman at Drake who’d seen another Sanders speech. “He gets to the point of what people want. He’s right about tuition costs.”

But Vivanh wasn’t sure what Sanders meant when he talked about his broader ideology. “Democratic socialist . . . I don’t really know what that means,” Vivanh said. “It sounds like he’s more focused on society. Is that what it means?”

Sanders has been in elected office for 34 years now. For that entire time, he has been arguing with people about whether the word “socialist” applies to him — and what he thinks socialism actually means.

In 1981, when Sanders ran for mayor of Burlington as a far-left independent, he was tagged as a socialist by his enemies. Sanders embraced the term, said his longtime friend Stanley “Huck” Gutman, partly as a way of showing his dislike for the two mainstream parties.

“The Democratic Party has too often been complicit in not serving the people who vote for the Democratic Party. I think the Democratic Party pays too much attention to Wall Street,” said Gutman, a poetry professor at the University of Vermont who has also worked as Sanders’s chief of staff in Congress. “I know Bernie certainly thinks so.”

As mayor, Sanders gave his small city a “foreign policy,” and it was decidedly leftist. He visited Nicaragua to meet Sandinista leaders. He spent his honeymoon on a goodwill trip to Burlington’s sister city in the Soviet Union.

He was elected to Congress, in 1990, and seemed to relish his role as a skunk at the two parties’ picnic.

“What do you think of socialism?” Sanders asked passersby outside the Capitol on his first day, according to a story in the Boston Globe. “What happens if we were in France? Does that panic you? Would you be afraid to go to France?”

But in the years since, Sanders has blurred the lines between himself and Democrats. First he joined their caucus in Congress. Now he’s running for president in their primary. And, when he talks about what a “democratic socialist” is, he does not emphasize that old opposition to the two-party system.

In this campaign, in fact, some observers believe that Sanders is even wrong to call himself a “democratic socialist.”

That’s because there are official Democratic Socialists — both in other countries and in the United States — and they generally want something more aggressive than he does. The Democratic Socialists in the United States want a system where workers or the government own factories and other means of production. (This is different from a communist system, in which the government owns everything in the people’s name.)

Sanders doesn’t want that. Instead, what he wants is to take existing federal programs — many established by Democrats such as Franklin D. Roosevelt or Lyndon B. Johnson — and super-size them.

Right now, for instance, the federal government provides health insurance to seniors: Medicare. Sanders wants the government to start providing it to everybody, a national single-payer system that might cost something like $15 trillion.

For another current example, government — federal, state and local — pays for public school for every child who wants it. Sanders wants to expand that to both younger and older students. He would make preschool universal and make public college tuition-free. In the process, he’d be giving Washington unprecedented new levels of control over these sectors.

“He’s not a democratic socialist,” said William Galston, an expert on domestic politics at the Brookings Institution. “He’s a social democrat. Seriously.”

Social Democrats, a separate entity in the field guide to leftists, are generally more moderate. By those definitions, then, Sanders is actually making his own life harder, by mislabeling himself.

Still, socialism is the label he’s stuck with. Sanders’s friends worry about what’s coming: future attack ads aimed at that 50 percent of Americans who wouldn’t vote for a socialist at all.

So far, the toughest thing he’s faced was a mild rejoinder from Hillary Rodham Clinton at the first Democratic debate.

“We are not Denmark. I love Denmark. We are the United States of America,” Clinton said, after Sanders cited Denmark as an example of democratic socialism in action.

She didn’t even use the s-word. Yet.

Fahrenthold reported from Washington. John Wagner in Goffstown, N.H., contributed to this report.