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Media captionMr Sanders got personal as he rounded on President TrumpUS Senator Bernie Sanders has launched his bid to be president in 2020 with an attack on corporate greed and a promise to unleash a “political revolution”.
Speaking in Brooklyn, New York, he called Donald Trump the “most dangerous president” in recent US history.
Mr Sanders, a 77-year-old independent senator for Vermont, lost the 2016 Democrat race to Hillary Clinton.
He faces a much more crowded field this time but brings name recognition and a passionate support base.
More than 10 others are also running to be Democrat candidate, including Massachusetts Senator Elizabeth Warren, New Jersey Senator Cory Booker and the Mayor of San Antonio, Texas, Julian Castro.
What would a Sanders presidency look like?
His speech promised a presidency that would “bring people together”. He outlined numerous policies and attacked greed and the “billionaire class”. As president, he said he would:
Enact a “federal jobs guarantee” to ensure all Americans have work
More than double the minimum wage from $7.25 (£5.50) to $15
Pass “comprehensive” immigration reform, including allowing hundreds of thousands of undocumented migrants to stay in the US
Make universities and colleges tuition-free
Reform healthcare to give universal coverage
He promised to fight for “economic justice, social justice, racial justice and environmental justice”.
Skip Twitter post by @BernieSanders
Today we say to the private health insurance companies, whether you like it or not, the United States will join every other major country on Earth and guarantee healthcare to all people as a right. #BernieInBrooklyn— Bernie Sanders (@BernieSanders) March 2, 2019
End of Twitter post by @BernieSanders
One of the challenges Mr Sanders faces is that the Democratic Party has shifted to the left, making his message less distinctive, BBC North America reporter Anthony Zurcher says.
Speaking to the BBC, Mr Sanders’s brother Larry said the Vermont senator was right to try again for the presidency.
“I think Bernard’s presidency would be really uplifting, finally to have somebody who people see as honest and has been committed for such a long time to be saying that we don’t need the poverty, we can have all the things that we need,” he said.
“It’s all been a kind of crazy dogma that ‘oh no, no, no, you can’t afford that’.”
What did he have to say about President Trump?
Mr Sanders was born in Brooklyn, and the backdrop for his speech gave him an opportunity to contrast himself with the president.
He grew up as the son of a Jewish immigrant who worked as a paint seller, while Mr Trump, who also was born in New York, was the son of a wealthy real estate developer.
“I did not have a father who gave me millions of dollars to build luxury skyscrapers, casinos and country clubs,” he said.
“But I had something more valuable: I had the role model of a father who had unbelievable courage in journeying across an ocean, with no money in his pocket, to start a new and better life.”
As he was speaking Mr Trump was addressing a conference of conservative activists, in which he attacked the Democrats and promised he would win re-election.
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He sarcastically mocked Democrat proposals on the environment and said plans for universal healthcare would lead to a “socialist takeover of American healthcare”.
Who is Bernie Sanders?
He is the longest-serving independent in congressional history, but competes for the Democratic nomination as he says standing as a third-party candidate would diminish his chances of winning the presidency.
He attended the University of Chicago, and in the 1960s and 1970s participated in anti-war and civil rights activism, like the 1963 March on Washington.
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In 1990, he became the first independent in 40 years to be elected to the House of Representatives. He served there until he ran for and won a seat in the Senate in 2007.
Mr Sanders entered the race for the 2016 Democratic nomination as a marginal candidate but emerged as a surprise star during a series of televised debates.
He labels himself a Democratic socialist, which he has defined as someone who seeks to “create an economy that works for all, not just the very wealthy”.
He became Mrs Clinton’s closest rival, but she ultimately won the nomination before losing the presidential election to Mr Trump.