It's dead, writes political scientist Adolph Reed Jr. The left in America is dead.

"Good!" would probably be the reaction of Al From, founder of the Democratic Leadership Council in the 1980s.

From has just published a self-congratulatory memoir about how he used the DLC to push the Democratic Party to the right and then into the White House in the 1990s, thus personally rescuing the party from itself.

Reed's essay "Nothing Left: The long slow surrender of American Liberals" in this month's Harper's magazine is a critique of the very thing From celebrates in his book The New Democrats and the Return to Power.

For activists like Reed, an African-American who specializes in minority rights, the Democrats have become the party of the sellout.

They have adopted conservative orthodoxies about small government, entitlement reform and taxes in exchange for electoral successes.

For the backroom strategist From, the Democrats had to move to the centre to survive. The rewards were the two-term victories of Bill Clinton and Barack Obama.

Now along comes the inconvenient fact of Bill de Blasio to upset both sides of the argument.

Unabashedly left

De Blasio was elected mayor of New York in November on a platform to raise taxes on the wealthy so that he could spend it on a new entitlement program for early childhood education.

He came from the middle of the pack to win the Democratic primary, and then handily won the mayoralty with 73 per cent of the vote.

He is well connected with the so-called new Democrats. He has worked for both Bill and Hillary Clinton and with New York's Governor Andrew Cuomo.

NYC Mayor Inauguration

Former president Bill Clinton administers the oath of office to Bill de Blasio in January 2014, as the new mayor's wife, Chirlane McCray, daughter Chiara and son Dante de Blasio look on. (Frank Franklin II / Associated Press)

But he is not quite one of them.

When former president Clinton swore him in as mayor, de Blasio read the oath with one hand resting on a Bible that had once been used by Franklin Roosevelt. That is the kind of throwback Democrat he intends to be.

He has made it the test of all his political goals that they be antidotes to the vast social and economic inequality in his city. He describes himself as a Roosevelt New Dealer with twenty-first century upgrades.

At the city level, de Blasio's political hero is Fiorello LaGuardia, the progressive Republican who was mayor of New York from the Depression in the 1930s through the Second World War.

LaGuardia was also a New Dealer who believed in a big role for government in society. (Bill Clinton, remember, famously declared the era of big government "over.")

On The Daily Show with Jon Stewart recently de Blasio gamely offered a send-up of his own image: "I don't wear the Che Guevara T-shirt at work," he joked.

It was a self-parody, but chances are, tucked away somewhere, de Blasio really does have a T-shirt emblazoned with the iconic portrait of the Marxist revolutionary.

He is certainly more left than any mayor since LaGuardia who is still widely regarded as the best mayor the city ever had.

"Every mayor wants to be like LaGuardia," says LaGuardia's granddaughter, Katherine. "Bill de Blasio is the first mayor to come along who I think has the possibility to do that."

Man of the millennials?

As a young man in the 1980s, de Blasio was an active supporter of Nicaragua's socialist Sandinistas.

He raised money for them and he toured Nicaragua distributing food and medical supplies. (At the time, the Reagan administration was arming and training the anti-Sandinista Contras.)

In 1990, when asked about his worldview, de Blasio said he advocated "democratic socialism."

After he married in1994, he and his new wife flouted an American travel ban and took off on a honeymoon to Cuba.

There was a time when such details might have doomed a candidate for public office in America.

YE May Day Protests NYC

A New York police lieutenant swings his baton at Occupy Wall Street activists during the 2012 May Day March on Wall Street. Will de Blasio's election change the dynamic that sparked the Occupy movement in the first place? (The Associated Press)

But the times they are a-changing, as someone once sang.

New York's mayoral election was the first since the Occupy movement drew worldwide attention to the vast inequality in America's social and economic life. And de Blasio connected with the Occupy complaint.

He campaigned against the Tale of Two Cities — the city of the one per cent from whence came the outgoing mayor, billionaire Michael Bloomberg of the Upper East Side, and the city of everyone else.

De Blasio was "the everyone else" candidate from Park Slope in Brooklyn.

Democrats, who are excited by him because they see him as both a genuine progressive and a winner, see something else even more thrilling down the road.

De Blasio appeals strongly to what is fast becoming the largest cohort of voters since the baby boom, the so-called millennials, who came of age around the turn of the century, and are in their 20s and early 30s.

Generations can come and go without representing anything remarkable, but the millennial cohort seems destined to have more impact than others.

The searing experiences for American millennials have mostly been in the dark early years of this century, including the 9-11 attack, the foreign wars, the government's failure to look after the victims of Katrina, and the worldwide collapse of the financial system.

If this is the world you've grown up in, how does that affect your politics?

It might make you want to turn your back on the whole mess, but millennials, it seems, are actually quite upbeat.

They are also, according to a 2010 Pew Research study, more likely than previous generations to believe in a role for government in their lives, and are markedly more comfortable with the idea of socialism.

Their values are different. Their highest priority isn't home ownership or having a career that pays well, it is to be good parents and have a good marriage, according to Pew.

Also, they are more likely to be liberals. And they have tattoos.

None of these things is true for every single millennial, of course, but it should encourage progressives to believe there is a new emerging and receptive audience for their message.

This audience is unlikely to be the "new Democrats" who were attracted to Clinton and Obama, but they might be Democrats anyway.

We may one day look back and call them the Bill de Blasio Democrats.