WASHINGTON • It used to be that socialism was a dirty word in the United States and conjured up images of Venezuela's Hugo Chavez or the brutal dictatorship of Joseph Stalin in the Soviet Union.

The word "socialist" has also been used as an insult against US President Barack Obama, while the healthcare reform known as Obamacare has been condemned as "socialised medicine".

It is thus mind-boggling that someone who is a self-avowed "Democratic Socialist" is now giving former secretary of state Hillary Clinton an almighty run for her money in the race to be the presidential nominee of the Democratic Party.

After the first three contests in the US primary season, the once presumed Clinton coronation has been all but cancelled. Despite holding a double-digit lead in the popularity polls for six months, Mrs Clinton watched nearly all of it evaporate in the face of an insurgent campaign from Vermont Senator Bernie Sanders last month.

The two ended in a virtual tie in the Iowa caucus on Feb 1. A week later, Mr Sanders clobbered Mrs Clinton by 22 points in New Hampshire. Mrs Clinton then saved some face in Nevada last week, with a narrow victory.

The rise of Mr Sanders has been the source of some amusement for the Republican Party, which is facing a troubling insurgent campaign of its own.

The party that had been preparing for a tough battle with Mrs Clinton believes Mr Sanders would be an easier candidate to defeat. And, indeed, observers agree that just having a "socialist" as the flag-bearer of the Democratic Party - regardless of what his policies might be - would be highly motivational for the conservative Republican base.

The question is, thus: Why is Mr Sanders doing well and what does his rise say about politics in the US? Is the motherland of capitalism suddenly turning its head towards socialism?

WHAT IS DEMOCRATIC SOCIALISM?

A useful place to start figuring out the apparent rise of socialism in the US is to try and understand what democratic socialism is in the first place.

That is, of course, something easier said than done.

One of the few books offering an explanation of the ideology - Democratic Socialism: A Global Survey by Donald Busky - itself notes the struggle to find a consensus definition.

For instance, it noted the disagreements over whether democratic socialism and social democracy are the same thing.

Following the US campaign, one might come to assume that the two are interchangeable, but Mr Busky - formerly a prominent member of the democratic socialist organisation known as Socialist Party USA - contends that they are not.

"Social democracy is a somewhat controversial term among democratic socialists. Many democratic socialists use social democracy as a synonym for democratic socialism, while others, particularly revolutionary democratic socialists, do not; the latter seeing social democracy as something less than socialism - a milder, evolutionary ideology that seeks merely to reform capitalism," he writes.

Democratic socialism, he says, is the "wing of the socialist movement that combines a belief in a socially owned economy with that of a political democracy".

In short, it appears that while social democracy embraces capitalism but seeks to humanise it through state intervention, democratic socialists want to replace the privately owned profit-driven economy with one that is socially owned.

The website of the Democratic Socialists of America, a pro-Sanders outfit, elaborates on the idea of social ownership, stressing that while they do not want the government to own everything, they don't want big corporate bureaucracies to do so either.

"Social ownership could take many forms, such as worker-owned cooperatives or publicly owned enterprises managed by workers and consumer representatives. Democratic socialists favour as much decentralisation as possible," it said.

If you are trying to plot countries, Scandinavian countries are all considered social democrats, while there isn't a good example right now of a democratic socialist country. Singapore, despite some socialist elements, doesn't fit properly into any particular category.

(Free universal healthcare for those under the Pioneer Generation scheme would be embraced by democratic socialists, but they would likely baulk at the idea of means testing or a privately run public transport system.)

WHAT TYPE OF SOCIALIST IS SANDERS?

From everything the candidate has said on the stump and the policies listed on his website, it is tough to pin down Mr Sanders' ideology.

He may say he is a democratic socialist but his policies deviate from the ideology in some important ways.

For instance, he says he does not want the state to own and run everything.

"I don't believe government should own 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," he said during a speech in Georgetown University last year, in what remains the senator's lone attempt to outline his political ideology. "I believe in private companies that thrive and invest and grow in America, instead of shipping jobs and profits overseas."

That sounds closer to the Scandinavian model of social democracy.

Yet, in other ways, his plans go beyond the Finlands and Swedens of the world.

Experts who have studied Mr Sanders' tax proposals say the plans would increase tax rates across the board, including doubling the tax rate for top income earners. He also wants to increase the top marginal tax rate on capital gains to 64.2 per cent - significantly higher than those in western Europe which average in the 30s and 40s.

The tax hikes, he says, are to pay for programmes like free universal healthcare and free college tuition. His healthcare plan has been particularly contentious, with many analysts arguing that it amounts to making the government pay for the entire system - a degree of centralisation that other social democracies do not deploy.

It led one expert, Princeton University sociology professor Paul Starr, to issue the warning that the Sanders revolution includes "endorsing taxes at confiscatory levels and proposing a health plan that would effectively nationalise a sixth of the economy".

As far as foreign policy goes, Mr Sanders has thus far not explained how his brand of democratic socialism extends, apart from supporting coalition building in the Middle East and a strenuous objection to the Trans-Pacific Partnership free trade pact.

WHY IS HE DOING SO WELL?

The first thing to note about Mr Sanders' success is that it is not an indication that Americans are slowly but surely shifting away from capitalism and towards socialism.

Rather, as statistician Nate Silver contends, one big reason Mr Sanders hasn't suffered for his political label is that the term "socialism" is slowly losing its sting. While those who grew up in the Cold War flinch at the mention of the word, younger Americans do not carry the same baggage. Not surprisingly, Mr Sanders beats Mrs Clinton handily among young voters, but loses older voters to her.

But the fading of the word's stigma doesn't amount to supporters embracing the principles of socialism. Polls generally show no desire among Americans - even the young - for a significant expansion of government or any move to reduce income differences by using tax hikes to redistribute wealth.

Their support for Mr Sanders stems instead from the ways the candidate's persona and message have been tailored to tap disdain for the establishment.

If there is one clear message from American voters this year, it is that they no longer trust the political establishment. It is this anger that has propelled the campaigns of outsiders like Mr Donald Trump and Mr Sanders. The electorate has grown weary of gridlock in Washington and the influx of money into politics, and Mr Sanders' refusal to receive donations from large corporate donors strikes a chord. That Mr Trump is doing better than Mr Sanders is simply down to the fact that Republican voters are angrier than Democratic Party ones.

Mr Sanders has also been careful to frame his socialist message as one that wants to narrow income inequality and break up the big banks. He is careful to rail against enemies like corporations and the political establishment, without ever diving into the weeds about how exactly he intends to tackle those problems.

During his Georgetown University speech, he outlined his vision like this: "Let me define for you, simply and straightforwardly, what democratic socialism means to me... Democratic socialism means that we must create an economy that works for all, not just the very wealthy."

Put that broadly, it is a message that resounds with someone, whether socialist or not. If voters were to dig deeper, it would be interesting to see if the enthusiasm remains.

So, while an avowed socialist is doing well in the US, socialism - however one defines it - isn't about to unseat American capitalism any time soon.