Bernie Sanders, the 77-year-old senator from Vermont, has announced he is running for U president for a second time, entering a crowded field of candidates vying for the Democratic Party nomination to take on President Donald Trump in 2020.

Mr Sanders, who challenged Hillary Clinton for the party’s nomination in 2016, announced the decision on Tuesday, claiming that his policies were now supported “by a majority of Americans”.

“Three years ago, during our 2016 campaign, when we brought forth our progressive agenda we were told that our ideas were ‘radical’ and ‘extreme,’” he said in an email to supporters.

“Well, three years have come and gone. And, as result of millions of Americans standing up and fighting back, all of these policies and more are now supported by a majority of Americans.”

Asked about Mr Sanders’s run, Mr Trump said he wished him well, noting that he was “not treated with respect” by Mrs Clinton. But he said he believed that the senator had missed his time, despite the two men “sort of” agreeing on trade. “The problem is he doesn’t know what to do about it. We’re doing something very spectacular with trade.”

Mr Sanders for his part called Mr Trump “the most dangerous president in modern American history”, describing him as a “pathological liar, a fraud, a racist, a sexist, a xenophobe and someone who is undermining American democracy as he leads us in an authoritarian direction.”

But he said his campaign was “not only about defeating Donald Trump”.

I'm running for president. I am asking you to join me today as part of an unprecedented and historic grassroots campaign that will begin with at least 1 million people from across the country. Say you're in: https://t.co/KOTx0WZqRf pic.twitter.com/T1TLH0rm26 — Bernie Sanders (@BernieSanders) February 19, 2019

“Our campaign is about transforming our country and creating a government based on the principles of economic, social, racial and environmental justice,” he said.

Six candidates

Mr Sanders is the sixth member of the US Senate to date to announce a bid for the Democratic nomination next year. Corey Booker from New Jersey, first-term senator Kamala Harris, Kirsten Gillibrand, Minnesotan senator Amy Klobucher and Elizabeth Warren, a candidate who shares similar policy positions to Mr Sanders, have all launched campaigns.

Mr Sanders announced his candidacy at the time when the socialist wing of the Democratic Party appears to be on the ascendant, with figures like Alexandria Ocasio-Cortez, a new congresswoman from New York, embracing left-wing policies that have been supported by many in the party.

But his decision to run may spark fears of a return to the divisions that characterised the 2016 Democratic primary campaign.

Mrs Clinton, who ultimately lost the presidential race to Mr Trump in November 2016, laid much of the blame for her defeat at Mr Sanders’s feet.

In her post-election book What Happened , Mrs Clinton said that his attacks on her during the primary campaign did “lasting damage” and paved the way for Mr Trump’s demonisation of her during the campaign.

But in an interview with Vermont Public Radio on Tuesday morning, Mr Sanders said that this campaign would be very different to the last. “This time there may be 10, 15, 20 candidates so that makes it a very, very different campaign with a different set of challenges.”

The early Democratic primaries to choose the party’s nominee for 2020 are still a year away, with Iowa due to hold its caucus in early February 2020.

Several other potential candidates are expected to launch bids before then, with speculation surrounding former vice-president Joe Biden and former Texas congressman Beto O’Rourke. Both candidates are likely to tread more centrist ground in a bid to win over swing Republican voters.

Legal action

Meanwhile, 16 states have taken legal action against Mr Trump’s decision last week to declare a national emergency over immigration.

The lawsuit, California et al v Trump et al, which was filed in the federal district court in San Francisco, argues that Mr Trump does not have the power to divert funds to build a wall on the Mexico border as Congress controls spending, accusing the president of using the pretext of a “manufactured crisis of unlawful immigration”.

Mr Trump said he expects to do “very well with the lawsuit”, calling it an “open and shut case”.