US Senator Bernie Sanders says he will run again for president in 2020, making a second attempt to win the Democratic Party’s nomination.
The 77-year-old Vermont senator became a progressive political star in 2016 although he lost his candidacy bid.
In an email to supporters, he said it was time to complete the “political revolution” they had started.
An outspoken critic of President Donald Trump, Mr Sanders has described him as a “pathological liar” and “racist”.
Mr Sanders – an independent who caucuses with the Democrats – is one of the best-known names to join a crowded and diverse field of Democratic candidates, and early polls suggest he is far ahead.
His calls for universal government-provided healthcare, a $15 national minimum wage and free college education electrified young voters, raised millions of dollars in small donations and are now pillars of the party’s left-wing.
Mr Sanders, who lost the 2016 Democratic primary to former Secretary of State Hillary Clinton, said in his email: “Three years ago, when we talked about these and other ideas, we were told that they were ‘radical’ and ‘extreme’.
“Together, you and I and our 2016 campaign began the political revolution. Now, it is time to complete that revolution and implement the vision that we fought for.”
Elizabeth Warren, Kirsten Gillibrand, Kamala Harris, John Delaney and Julian Castro are among those who have also announced their intention to run in the Democratic primary in 2020, the first time more than one woman has competed.
If Mr Sanders is successful in his bid, he will become the oldest presidential candidate in US history.
In his email, which lays out a series of policy issues, Mr Sanders also says: “You know as well as I do that we are living in a pivotal and dangerous moment in American history.
“We are running against a president who is 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.”
Who is Bernie Sanders?
Mr Sanders 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 antiwar and civil rights activism, like the 1963 March on Washington.
He was first elected to the House of Representatives in 1990, the first independent to achieve such a feat in 40 years. 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 long-shot 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”.
Mr Sanders also has a diplomacy-first attitude towards foreign policy and voted against the US invasion of Iraq in 2002.
He became Mrs Clinton’s closest rival, but she ultimately won the nomination before losing the presidential election to Mr Trump.
In January, Mr Sanders apologised to female staff members on his 2016 campaign after allegations of harassment emerged.
Several aides complained of a “predatory culture” in his campaign and alleged that senior male staff had mistreated younger workers.