US SENATOR BERNIE Sanders, whose insurgent 2016 presidential campaign reshaped Democratic politics, has announced that he will run for president in 2020.

The 77-year-old self-described democratic socialist revealed the news today, saying his aim was to do more than defeat incumbent president, Donald Trump.

“Our campaign is about transforming our country and creating a government based on the principles of economic, social, racial and environmental justice,” Sanders said in an email to his supporters.

He won more than 13 million votes and dozens of primaries and caucuses in 2016, when he was seen as Hillary Clinton’s main rival for the Democratic nomination.

A progressive who embraces proposals such as Medicare for All to free college tuition, Sanders stunned the Democratic establishment in 2016 with his spirited challenge to Hillary Clinton.

While she ultimately became the party’s nominee, his campaign helped lay the groundwork for a recent leftward lurch that has dominated Democratic politics.

However, the run-up to today’s announcement has seen persistent allegations of sexual harassment of women by male staffers during Sanders’ 2016 campaign.Politico and The New York Times have reported several allegations of unwanted sexual advances and pay inequity.

In an interview with CNN after the initial allegations surfaced, Sanders apologised but also noted he was “a little busy running around the country trying to make the case”.

As additional allegations emerged, he offered a more unequivocal apology.

“What they experienced was absolutely unacceptable and certainly not what a progressive campaign – or any campaign – should be about,” he said on Capitol Hill last month.

“Every woman in this country who goes to work today or tomorrow has the right to make sure that she is working in an environment which is free of harassment, which is safe and is comfortable, and I will do my best to make that happen.”

Crowded field

There are also questions about whether Sanders can stand out in a crowded field of Democrats, who embrace many of his policy ideas and are newer to the political stage.

Senator Kamala Harris of California, another Democratic contender, appeared to take a dig at Sanders as she announced her intention to run in New Hampshire on Monday.

“The people of New Hampshire will tell me what’s required to compete in New Hampshire,” she told shoppers at a book shop in Concord.

“But I will tell you I’m not a democratic socialist.”

Senator Elizabeth Warren – seen as having similar goals to Sanders – has already launched her campaign and has planned a swing through the early primary states.

Shortly after announcing her exploratory committee, Warren hired Brendan Summers, who managed Sanders’ 2016 Iowa campaign.

Presidential candidate Elizabeth Warren at a campaign rally in California on February 18. SIPA USA / PA Images SIPA USA / PA Images / PA Images

Other candidates likely to take the field include Senator Cory Booker of New Jersey, Amy Klobuchar of Minnesota and Kirsten Gillibrand of New York.

The field could also grow, with a number of high-profile Democrats still considering presidential bids, including former Vice President Joe Biden and former Texas Representative Beto O’Rourke.

‘Ideas and vision’

While Sanders has been working to lay the groundwork for a second campaign for months, it was unclear whether he will be able to expand his appeal beyond his largely white base of supporters.

In 2016, he struggled to gain the support of black voters, an issue that could become pervasive during a primary race that could include several non-white candidates next year.

Last year, Sanders’ wife Dr Jane O’Meara, who also served as his policy and press adviser, told TheJournal.ie that Sanders would have offered voters a better alternative to Donald Trump in 2016.

“He would have beaten Trump, because people vote for someone with ideas and a vision, rather than with somebody who is negative,” she said.

“We saw signs of [Trump's win] beforehand – but Trump was a pointed disruption rather than a different vision for the future.”

With additional reporting from Associated Press and Gráinne Ní Aodha.