It’s late September in the picturesque city of Burlington, in Vermont, and the famous New England fall is not yet in its full autumnal glory. Along the shores of Lake Champlain the sun is beating down, the leaves are beginning to turn, and the atmosphere in this hipster student town is unmistakably laid back.

This is Bernie Sanders territory. The veteran left-wing US senator and presidential hopeful moved to Burlington, an hour south of the Canadian border, in the mid-1960s, part of a wave of east-coasters who moved to the rural state in search of something new.

The hippy vibe is still in full swing. Along the main thoroughfare – pedestrianised during Sanders’s time as mayor – classical music plays from speakers as people relax outside cafes and restaurants, soaking up the late-September sunshine.

I’m here to meet Jane O’Meara Sanders, the senator’s wife and political adviser, at the headquarters of the Sanders Institute, a nonprofit set up to promote progressive ideas and policies that grew out of his 2016 campaign.

I used to make fun of people who talked about going home and all that, but I just teared up when I saw Ireland. I felt a kinship

Softly spoken but quietly passionate, Jane Sanders is off to Limerick next week to speak at I.NY, a new festival celebrating the relationship between Ireland and New York.

Like millions of Americans, she grew up in an Irish-American household. The youngest of five children, Sanders was born in Brooklyn, growing up just 10 blocks from the man who was to become her future husband, although they were not to meet until years later. Her paternal grandfather emigrated to the United States from Tipperary, and three of her great-grandparents came from Ireland. “It’s funny. None of my parents’ generation had been to Ireland,” she says. “My generation went to check it out and fell in love with it.”

Reminders of her Irish heritage framed her childhood. A Sacred Heart hung on the wall, she went to Catholic schools, and both her father and grandfather were members of the Friendly Sons of St Patrick, the oldest Irish-American association in North America.

But it was only when she travelled to the old sod for the first time, in 1985, that she appreciated her heritage. “Visiting Ireland reminded me of when I first arrived in Vermont. I thought, This is home.” She and Bernie had been visiting his brother, Larry, still a Green Party activist in England, and took the ferry to Ireland. “As soon as my feet hit the ground I said, ‘Yes, this is it.’ ”

“I used to make fun of people who talked about going home and all that,” Sanders says with a smile. “I hadn’t really thought about it at all, but I just teared up when I saw Ireland. I felt a kinship.”

Political wife: Jane Sanders in 2016, during her husband’s campaign. Photograph: TJ Kirkpatrick/Bloomberg

‘Our eyes met’

But it was Jane’s meeting with Bernie that defined much of her life.

She moved to Burlington in the 1970s with her first husband, who had relocated there for work. She first encountered Bernie when he was running for mayor and she was working as a community activist. “I was sitting in the second row, and our eyes met, but we didn’t really talk afterwards.” But she was captivated. “I felt it came from the heart, everything he said. He embodied everything I ever believed in.”

It was not until their fourth meeting, at a party celebrating his election as mayor, in 1981, that they got together. They married in 1988. “He asked me to dance, and we’ve been together ever since,” she says, smiling. So began a marriage of minds as well as of hearts, as Sanders became a constant figure by her husband’s side as he built his political career.

In 1988, when he was approaching his eighth year as mayor of Burlington, Bernie ran for Congress. He was unsuccessful. Two years later he contested a seat again, this time winning by 10 points, and finally moving to Washington, DC, to represent the citizens of Vermont as an Independent.

Sanders was centrally involved with his career from this time, first through her own work as a community activist and eventually more formally, becoming his head of press in 1990.

In 1995, with her three children all working or at college, she also went down to Washington, setting up the Congressional Progressive Caucus and becoming her husband’s chief of staff.

Political couple: Jane and Bernie Sanders in Washington in 1990. Photograph: Michele McDonald/Boston Globe

‘You have to do it’

In 2006 Bernie was elected to the US Senate, a move that Sanders says significantly enhanced his national profile. But even then few would have believed the socialist would set his sights on becoming president of the United States.

When did the plan to run in 2016 come about?

“As the election approached people started asking him, [saying] you should run, you should run. He dismissed it, and so did I, but in 2015 we were waiting to have a debate about the ideas and it became very apparent to us that nobody was going to have a debate in the Democratic primaries. To us that was crazy,” says Sanders.

“We’ve known Hillary Clinton. She’s great, she’s wonderful, a very smart woman.” Both Sanders and her husband respect Hillary, she says, but “her politics are centrist”.

Despite “shaking the bushes” to find someone to run, Bernie began to think about running himself. The decision was finally made one morning, as they were having breakfast, and were approached by a Vietnam veteran.

“He explained that he had been a victim of Agent Orange” – a dangerous defoliant the US used in the Vietnam War – “and while he had fought for 30 years to get benefits, he didn’t succeed until he worked with Bernie’s office. He said he hoped Bernie would run for president. I just teared up. Bernie stood up and shook his hand, I hugged him, and I said: ‘You have to do it. It’s not about us. How can we not?’ ”

What followed was one of the most divisive primary campaigns in recent American history, as Bernie Sanders took on Hillary Clinton for a nomination that many in the party believed was hers for the taking, opening up wounds in the Democratic Party that have yet to heal.

Political couple: Jane and Bernie Sanders campaigning in 1992. Photograph: Bernie Sanders Campaign

‘The wrong candidate’

Sanders outperformed virtually all analysts’ expectations, commanding huge crowds and invigorating young voters through his promise of a left-wing vision for American society, predicated on the right to healthcare, education and housing.

Tensions between the Sanders wing and the Democratic establishment erupted in May 2016 amid accusations that the Democratic National Committee, the party’s executive, conspired to put Clinton on the ticket over Bernie Sanders, after leaked emails showed DNC staff disparaging the Vermont senator.

Ugly scenes followed at the Democratic selection convention, in Philadelphia, where Bernie’s supporters, reluctant to back Clinton as the party’s nominee, shouted, “We want Bernie.”

Clinton has criticised him in the aftermath of the election. In What Happened, her new book, she accuses her primary opponent of laying the ground for Trump’s attacks on her.

Did Bernie ultimately cost Clinton and the Democratic Party the election, depriving the United States of its first woman president and helping to elect Donald Trump?

I don’t think Bernie stood in the way. I think Clinton would have lost to Trump anyway, because she was the wrong candidate at the time

“I disagree with that,” Jane Sanders says. “That’s democracy. There should always be primaries. It wasn’t that she was an incumbent. It’s nobody’s turn until it’s somebody’s turn; until the people decide it’s somebody’s turn.”

“Bernie never ran a negative campaign in his life,” she says. The Clinton campaign might dispute this, given his relentless focus on Clinton’s ties to Wall Street during the primary campaign. Of Clinton’s recent criticisms of her husband, Jane pauses, before saying: “It’s unfortunate.”

She is unequivocal that Clinton was a bad choice of nominee. “I don’t think Bernie stood in the way, as I think she would have lost to Trump anyway, not because she should have but because she was the wrong candidate at the time,” Sanders says.

“There was a sense in the country, that we felt palpably from people, that, yes, we’ve made progress in some areas, but many of us have been left behind, and nobody is speaking to us. “Also, [there was a] sense that the Clinton campaign was a third term for Barack Obama. There is nothing wrong with that, but that’s not what they wanted at that time, and that’s not what they want now.

“I think the American people, through the healthy exchange of ideas, understood that they could do better as a country, in terms of healthcare, affordable education, affordable housing. Bernie was the candidate for change, Trump was the candidate for change, and Secretary Clinton was the candidate for keeping steady on the path. That was not what the American people were looking for.”

Campaign trail: Jane Sanders sits backstage at a rally in 2016. Photograph: Sam Hodgson/New York Times

‘He would have won’

Does she believe Bernie would have beaten Trump? “I think he would have won. I have very little doubt he would have won,” she says, “because American people wanted change and they weren’t willing to vote for the status quo.”

She notes that, throughout the primaries, working-class white voters, who in the end voted for Trump, supported Bernie. Even though her husband lacked support among African-American voters, under-40s in every constituency, including black and Latino, voted for him, she says.

Bernie was also critcised by many in the Democratic Party for not pulling out earlier from the campaign. Sanders disputes that, pointing out that Clinton didn’t pull out during her primary contest with Obama, before the presidential election of 2008, until the end.

Sanders recalls how she and her husband met Clinton in a hotel room in DC to announce he was withdrawing, and they had a “very good discussion”, focusing on healthcare and on free tuition for public colleges and universities.

Bernie didn’t feel he had the opportunity to stop: this is not the time to lay back, relax and pay attention to ourselves; we have to go out and fight

“The one thing that does bother me, considering how hard he worked in having her win the election, are the untruths – Hillary’s claim that she didn’t get the same respect from her opponent as she gave to Barack Obama. During the convention we went to every event – each state that we won held a breakfast – because Bernie felt so strongly that Donald Trump could not become president.”

She says that in the final week of the presidential campaign her husband had more events than Clinton, whose team took the result “for granted. They thought they had it won. They had two great parties, two nights before the election: Bon Jovi and Beyoncé. And Bernie was out in California, trying to pass proposition 61” – a drug-pricing measure – “as well as running around the country.”

Sanders is critical of Clinton’s attitude since the defeat. “Most people who run for president, if they don’t win the primary, or even if they don’t win the election, they just disappear. I mean, Secretary Clinton says in her interviews, ‘I drank a lot of wine, saw a lot of theatre, read a lot of good books.’ The Trump administration was going on. Bernie didn’t feel he had the opportunity to stop: this is not the time to lay back, relax and pay attention to ourselves; we have to go out and fight. He’s never stopped from the time he didn’t win the primary.”

Presidential campaign: Bernie and Jane Sanders in 2016. Photograph: Sam Hodgson/New York Times

Her phone rings. It’s Bernie

Sanders’s commitment to her husband and to the left-wing politics he has made his life’s work shines through. At one point her phone rings – it’s Bernie, from Washington, who the night before took part in a CNN debate on healthcare. She tells him she’s talking to The Irish Times. “Love you,” she says as she ends the call; he had only rung for a chat, she says.

But, despite their closeness, Sanders’s role in her husband’s political life has not been without its problems. Her tenure at the helm of Burlington College, a small private college, has come under scrutiny in recent months. She resigned in 2011, and the school closed in 2016, under mounting debts.

A land deal agreed under Sanders’s watch is now under federal investigation. Sanders says that she is entirely innocent and that the campaign against her is politically motivated.

She mentions the current vice-chairman of the Republican Party in Vermont, who also headed Trump’s campaign in the state. “That’s what he does here, what he has done to the state attorney several times, and to progressives. He constantly makes charges, and then people have to follow through and investigate, to be able to say there is nothing there.” She says she will be exonerated by the investigation, which she expects to take a long time.

As we leave her office and walk down to the lake we talk about family life. Her son David Driscoll, who is executive director of the Sanders Institute, lives nearby. Bernie, who had a child from a previous relationship, and Sanders, who had three children from her first marriage, now have seven grandchildren between them. “Bernie is great with the grandkids. He teaches them how to play chess, baseball. They adore him.”

Trump has to be stopped

I ask if Bernie will run again in 2020. “We don’t know,” Sanders says, refusing to rule out a prospect that many in political circles now see as a real possibility. Both have just returned from a trip to California, which some suspect was a sign that Sanders is gathering support for another primary bid, although he will be 79 at the time of the next election.

But what she is clear about is her belief that Bernie’s campaign changed the conversation within the Democratic Party. As it continues to soul search in the wake of Trump’s improbable victory, the split between the centrist and more socialist wing of the party seems as strong as ever – as shown by the acrimonious battle this year to head the Democratic National Committee. (Bernie Sanders supported Keith Ellison, who lost to Tom Perez.)

Democrats are now mulling over the party’s strategy for 2020 and for next year’s midterm elections. The Bernie Sanders wing has grounds to feel confident. As Sanders and other commentators have pointed out, Bernie’s recently unveiled proposal for a single-payer healthcare system gained 16 cosignatories in the Senate last week. Two years ago it got zero.

I was watching all these people listening, and you could see they understood this was coming from deep inside him, not just some silly stump speech

As the battle for the heart of the Democratic Party intensifies, Sanders believes the conversation has changed. “We didn’t win the election, but I think we won the day – and we won the minds and hearts of a large number of people, especially young people, the future of our country.”

She recalls a moment during the primary campaign when Bernie was just beginning to get noticed nationally. “I was watching all these people listening – he was not well known across the country at this point – and you could see them just get it, that they understood that this was coming from deep inside him, not just some silly stump speech. And immediately I thought, I recognise that, I recognise that look. They’re feeling like I felt that time when I’d never talked to him but was just listening to him.”

As she reflects on the Trump phenomenon, she says it is now up to the Democratic Party to lead. “What we need to offer is a vision for the future that addresses the needs of the American people and the direction they want to go in. What Trump is doing is a lot more than just talking, tweets. He is rolling back regulations, standards, destroying lives. This has to be stopped. There has to be a sense of urgency, a really authentic sense of urgency, that we have not just got to fight but to lead.”