In January 2017, days before Donald Trump’s inauguration, Bernie Sanders appeared unexpectedly on stage at a rally in Macomb county, Michigan, a perennial political battleground in a state that had slipped from the Democrats’ grasp. The crowd began to stir. A woman shrieked.

The Senate minority leader Chuck Schumer, who at that moment was in the middle of a fiery denunciation of Republican efforts to repeal the Affordable Care Act (ACA), looked up. Peering over his half-moon glasses, he saw the Vermont senator, the New Yorker’s “brother from Brooklyn”, had arrived ahead of schedule.

Schumer gestured frantically that Sanders should wait. But it was too late. The senator, with his unruly mop of white hair, had been spotted.

A familiar chorus began: “Bernie! Bernie!”

Hillary Clinton won the popular vote and Trump won the presidency but in Warren, Michigan, the crowd wanted the independent Democratic socialist whose long-shot presidential bid captured the imagination of a new generation of progressive leaders and activists.

Two years on, Sanders faces a decision that will likely determine the arc of his more than 40-year career.

It’s vitally important for this movement and for this country that he finishes what he started

Should he run again for president, as he has given every impression that he will, the 77-year-old senator would enter not as an ideological crusader with “pie-in-the-sky” ideas but as the leader of an ascendent movement and a top-tier contender not to be underestimated.

The possibility of a second run has hung over Sanders since Trump won. The senator has seemed to grapple for months with the decision, even as his team has moved to put the pieces in place for a presidential campaign. But the question has taken on a new urgency as the Democratic field fills with friends and colleagues.

“The people have finally caught up to Bernie Sanders,” said Nina Turner, the president of Our Revolution, the organization that grew out of his 2016 campaign. “It’s vitally important for this movement and for this country that he finishes what he started.”

Bernie Sanders six months after becoming mayor mayor of Burlington, Vermont’s largest city, in 1981. Photograph: Donna Light/AP

The political terrain has shifted remarkably since Sanders announced his run for president in April 2015, with little fanfare and from a grassy patch outside the US Capitol known as the swamp.

Many of the 2020 candidates have embraced Sanders’ most popular economic proposals, such as Medicare for all and a $15 minimum wage. He and his allies were also successful in reducing the influence of so-called super-delegates in the party’s presidential-nominating process, a source of controversy in 2016. And, now, majority of Democrats now consider themselves “liberal” and hold more a more positive view of “socialism” than of “capitalism”.

“In many ways, Sanders was the first to recognize that Trump’s strength was rooted in a kind of conservative populism,” said Celinda Lake, a longtime Democratic pollster. “He understood that you have to be populist to beat populism and, initially, he was the one who articulated most clearly progressive populism.”

‘It isn’t old vs new or progressive vs pragmatic’

No candidate enters the race with as many advantages as Sanders, who ended the 2016 primaries after winning more than 13m votes and raising nearly $230m, much of it through small-dollar donations. Should he run, he would start with near-universal name recognition, a loyal following, a digital media platform that reaches millions and an unrivaled donor list. Of the declared 2020 contenders, only Trump has more Twitter followers.

But Sanders is also now a known quantity with no chance of repeating the insurgent, expectation-shattering campaign of 2016. The race is likely to be more negative and he would almost certainly face more scrutiny. The Clinton campaign ran no attack ads against him during the 2016 primary.

“This time around,” Lake said, “he will be the one who has to worry about a surprise insurgent.”

Early polling suggests Sanders has lost some grassroots support. And in surveys conducted by the progressive Daily Kos website, Sanders has trailed senators Elizabeth Warren and Kamala Harris and former congressman Beto O’Rourke.

“His success in 2016 owed a lot to the contours of the race,” said Brian Fallon, the former national press secretary for Hillary Clinton. The voters who flocked to his campaign because they were wary of a “Clinton coronation” or who were disillusioned by party politics will likely have more than a dozen choices in 2020, Fallon said. And this time, there is no “establishment” favorite – at least not yet.

“It isn’t old vs new or progressive vs pragmatic anymore,” said Tom Vilsack, the former US secretary of agriculture who served two-terms as Iowa’s governor. “His challenge in Iowa is to maintain what he has.”

Sanders has remained one of the most popular politicians in America. Central to his appeal is the perception that like his accent, he has hardly changed since he left Brooklyn in the early 60s.

Like a well-worn record, Sanders has been railing against economic injustice and Wall Street greed since he started running for office nearly fifty years ago. And his early support for gay rights, opposition to international trade agreements such as the North American Free Trade Agreement (NAFTA) and a vote against the Iraq war cemented his image as an “uncompromised” progressive champion.

“There are very few people in politics right now as original as he is,” said Abdul El-Sayed, a former Democratic candidate for governor of Michigan.

El-Sayed ran with Sanders’ imprimatur but lost the primary. But he believes the movement is reshaping the party in profound ways. Weeks before the 2018 election, Sanders returned to Michigan to campaign for Gretchen Whitmer, who beat El-Sayed in the primary and went on to become governor.

There are no shortage of Democrats who do not want Sanders to be the party’s standard bearer in 2020. Many in the party say they would prefer a candidate fresh to the national political scene. While some say the long-serving Independent is more focused on waging internecine battles than leading the resistance to Trump. It’s a criticism his team believes is unfair: since the 2016 election, Sanders has joined Senate leadership, toured the Rust Belt with the Democratic National Committee (DNC) chair, Tom Perez, and fought to protect the ACA.

Tonight, we renew our resolve that America will never be a socialist country

Sanders also faces sharp opposition from those who believe his diagnosis is wrong and from the party’s centrists who say his liberalism threatens Democrats in conservative districts and battleground states.

In his state of the union speech on Tuesday, Trump sought to tap into such fears.

“We are alarmed by new calls to adopt socialism in our country,” the president said, as news cameras pivoted to capture Sanders’ reaction. “Tonight, we renew our resolve that America will never be a socialist country.”

The proclamation led to chants of “U-S-A” in the House chamber.

Sanders, stone-faced, rested his chin on his hand.

The primary will undoubtedly lay bare tensions within the Democratic party. The candidates are historically diverse: female, black, Hispanic, AsianAmerican, gay, millennial. And after an election cycle that saw a historic number of women and minority candidates elected, Democrats are excited for a new generation of leaders who represent the diversity of their base.

Early polling suggests Bernie Sanders has lost some grassroots support. Photograph: Andy Duback/AP

“The candidate who will be successful is the one who can speak authentically to a multiracial coalition of progressives in the name of racial, social, gender and economic justice,” said Aimee Allison, the founder and president of She the People, a group focused on electing women of color.

This is one area where Sanders has faced the most criticism from Democrats who say his class-based view of economic inequities downplays race and gender. The senator has spent two years working to strengthen relationships in communities of color, especially with black and Latino voters across the south and south-west he struggled to attract in 2016.

Bakari Sellers, a former state representative from South Carolina, doubted he would sway many black voters in the south.

“It’s hard for someone who doesn’t go to your school to want to come in and be captain of your football team,” he said.

Turner, the head of Our Revolution, said Sanders must do a better job of dispelling the notion that he doesn’t understand race and gender issues.

“He has to revisit his 20-year old self, the Bernie Sanders who was fighting at the University of Chicago, who was standing up against segregation – the Bernie Sanders who was there when Martin Luther King delivered his I Have a Dream speech,” she said.

Sanders was born in Brooklyn, New York, in 1941. His family lived in a small, rent-controlled apartment and struggled to get by on the low wage of his father, a Jewish immigrant from Poland who sold paint.

As a college student at the University of Chicago, Sanders joined the Young People’s Socialist League and was active in the civil rights movement. In 1968, he moved to Vermont, and shortly after made his first foray into politics.

The senator rarely speaks about his own life, his fist-thumping speeches typically devoid of the biographical threads Americans have come to expect.

Racial equality must be central to combating economic inequality

On a recent visit to South Carolina for Martin Luther King Jr Day, he tried a new approach.

“Racial equality must be central to combating economic inequality,” Sanders told a crowd on the steps of the state capitol. In his remarks, he recalled attending King’s historic speech and reminded them that its official name was the 1963 “March on Washington for Jobs and Freedom”.

‘Real accomplishment’

Sanders has sought to address other issues that were seen as shortcomings in 2016 – his record on gun rights and his lack of foreign policy expertise. In the Senate, he led an effort to end US support for the Saudi-led military operations in Yemen. In December, a handful of Republicans joined Democrats in passing the measure, which amounted to an unprecedented rebuke of the president.

Last year, in a Republican-controlled Washington, Sanders successfully pressured Amazon to raise minimum wages for hourly workers. He is now turning his attention to McDonald’s and Walmart.

“He can go into communities that have been left behind and say, “I raised wages for hundreds of thousands of American workers,’” said congressman Ro Khanna, a Democrat from California who joined Sanders in the effort. “That is a real accomplishment.”

Many 2020 candidates have embraced Sanders’ most popular economic proposals, such as Medicare for all and free college tuition. Photograph: Damian Dovarganes/AP

But Sanders also faces new challenges. He began the year with an apology to former female staffers after two waves of reports described harassment, sexism and gender discrimination in his 2016 campaign. As a result, a handful of aides and advisers will not be a part of a future campaign. And former campaign manager Jeff Weaver has said he will not return to the role if Sanders runs in 2020.

As a decision draws nearer, media speculation – or what Sanders derisively calls “political gossip” – has intensified. Did he miss his moment? Has he lost his spark? Is he too old? To all of these questions, his advisers and allies believe the answer is a resounding “no”.

Campaigning for candidates in 2018, Turner said he drew crowds as large and energized as ever. He was “tireless”, not tired, she said. And as for his age: “By their standard, Nelson Mandela would never have been president.” Mandela was 75 when be became president of South Africa. Sanders would be 78 when the Iowa caucuses are held in February 2020.

In recent weeks, Sanders’ legion of supporters have staged hundreds of gatherings in bars, coffee shops and living rooms across the country to draw him into the race — and soon.

“They’ve got the blue wave, we’ve got the tidal wave,” said RoseAnn DeMoro, the former executive director of National Nurses United.

DeMoro has supported Sanders for most of his political career. In 1981, she read about a self-described socialist running for mayor in Vermont and the California resident made her first donation to a Sanders’ campaign. Like many of his longtime allies, DeMoro is pleased to see the party warm to Sanders’ progressive populism. But for her, he’ll always be the original.