NEW YORK - US Senator Bernie Sanders kicked off his 2020 presidential campaign as a second-time runner on Saturday in his hometown borough of Brooklyn, New York, reiterating his Democratic socialist views that have been reshaping the Democratic Party.

On the snow-covered campus of Brooklyn College, Sanders, 77, expressed his determination to fight for a “Medicare-for-all” healthcare system and a 15-US-dollar hourly minimum wage, and vowed to address climate change and other priority issues that altogether form a progressive agenda.

The Brooklyn native recalled his childhood living in a rent-controlled apartment as the son of a Polish immigrant who came to the United States without a nickel, saying this experience has well connected him with today’s lower class.

“With your help, we are going to transform this country, and finally create an economy and a government which work for all of us, not just the one percent,” Sanders told thousands of enthusiastic supporters from New York and adjacent states, most of whom were millenials holding a colorful banner with “Bernie” written on it. “Bernie is a special type of candidate that you don’t usually see in U.S. politics. He’s really fighting for everyday people,” said 24-year-old local video producer Carl Straut-Collard. “I trust that he’ll be fighting for me and people who are less well-off.”

Representing the state of Vermont as an independent senator but caucusing with Democrats in Congress, Sanders was first elected to the House of Representatives in 1990 and to the Senate in 2006. He lost to Hillary Clinton after a tight race in the 2016 Democratic Party presidential primaries.

Meanwhile, 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. He promised to fight for “economic justice, social justice, racial justice and environmental justice”. 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’.” 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.

He sarcastically mocked Democrat proposals on the environment and said plans for universal healthcare would lead to a “socialist takeover of American healthcare”.

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.

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.