Today, Sanders is one of the most popular politicians among Democratic voters and his policy agenda - a suite of progressive proposals to expand health care, broaden the social safety net and make higher education free - has been embraced by numerous Democratic Party's leading figures. Cory Booker of New Jersey, Amy Klobuchar of Minnesota and Kirsten Gillibrand of NY.
"I wanted to let the people of the state of Vermont know about this first", Sanders said on Vermont Public Radio. "I think he is a pathological liar..."
He added, "I think the current occupant of the White House is an embarrassment to our country".
But he came close to pulling off the upset and ended up winning 23 primaries or caucuses against the better-funded Clinton. Political experts say that with numerous candidates, like Elizabeth Warren, carrying the same progressive message, it could make it harder for Sanders to separate himself from everyone else.
Sanders has reshaped Democratic politics and earned a loyal following with his passionate defence of liberal proposals including free college tuition and single-payer health care. "Now it is time to complete that revolution and implement the vision that we fought for", he said. She also appeared to take a dig at Sanders.
Trump's campaign weighed in on Sanders' run in a statement. "The world has changed".
Winter weather sticking around; light snow on the way
Shortly after the evening commute the first sleet pellets, snow flakes and rain drops arrive for the 77 corridor. Forecasters said another round of a wintry precipitation is possible Saturday night into Sunday .
Sanders, the son of Jewish immigrants from eastern Europe, was born and raised in Brooklyn.
After graduating, Mr Sanders worked on an Israeli kibbutz and moved to Vermont, where he worked as a carpenter and filmmaker.
For all his successes three years ago, 2020 will be a very different campaign cycle. He was re-elected in 2012 and 2018. Sherrod Brown of OH and former New York City mayor Michael Bloomberg, are also mulling bids for the Democratic nomination. Candidates like Sen. Elizabeth Warren of MA have already begun highlighting their progressive bona fides on the campaign trail, throwing their support behind bold proposals like Medicare for All and the Green New Deal while touting a tough stance on Wall Street.
Other staff from Mr Sanders's first bid have also said they would consider working for other candidates in 2020.
In an email to supporters shortly after the announcement, Sanders said: "Our campaign is about transforming our country and creating a government based on the principles of economic, social, racial and environmental justice". In a public apology last month, he denounced sexism and said the women's experiences were not part of "what a progressive campaign, or any campaign, should be about". "It must be a reality in our daily lives".
The Democratic Party will have its presidential candidates debate this summer. If successful, Sanders will be the oldest person ever elected to the White House. "I don't think it does, and I admire him", New Hampshire radio host Arnie Arnesen, a 2016 Sanders supporter, recently told NPR.