Mr Sanders has surpassed his rivals in early fundraising, earning $18.2m (£14m) in the first six weeks of the 2020 campaign, and has developed a sophisticated campaign team since his first run.
Following his 2016 campaign, he created the political group Our Revolution, which has collected information on voters and organised events in early voting states.
Mr Sanders won more than 20 primary contests against Ms Clinton in 2016 as a clear outsider and supporters argue popular demand for the senator's brand of self-described democratic socialism has not decreased.
"Donald Trump campaigned on economic terms as faux Bernie Sanders. It was taking his language and selling it to the American people," said Faiz Shakir, Mr Sanders' campaign manager.
"And now how do you defeat faux Bernie Sanders? You defeat him with real Bernie Sanders."
However, some Democrats worry weaknesses in Mr Sanders’ 2016 campaign remain, such as criticism that his team was too heavily white and male and concerns that his left-wing policy platform could turn away swing voters.
Despite enthusiasm for Mr Sanders' campaign, critics also say he performed poorly with black voters who overwhelmingly backed Ms Clinton in 2016.
Notably, Mr Sanders lost the South Carolina primary by more than 45 points.
"I understand that a lot of people took a lot of things out of the South Carolina results," Mr Shakir said.
"We are going to continue to court and address these issues directly, but we are operating with a great deal of confidence that this is going to be a particular demographic that supports Bernie Sanders at the end of the day."
Sanders advisers have argued he has addressed the weakness by working to build relationships with black leaders in South Carolina and other Southern states, while making racial inequality and criminal justice more prominent issues in his campaigning.
Campaign officials also argue that his 2020 team will be more diverse with current campaign staff reportedly being majority female and 40 per cent people of colour.
“We were criticised for being too white; that was a correct criticism,” Mr Sanders said on the Breakfast Club radio show in March.
“We were criticised for being too male; that was a correct criticism. That’s going to change.”
In early polling, Mr Sanders has shown his popularity from 2016 has not disappeared, as polling averages put him up to 10 percentage points above other declared Democrats.
However, he is still behind former vice-president Joe Biden, who has indicated that he is planning to run but has not formerly announced a campaign.
Critics also argue Mr Sanders' position in polling is partly due to name recognition at this point, with himself and Mr Biden being the two most well-known candidates.
While Mr Sanders has become a household name in US politics, he is not universally liked by Democrats, with some blaming him for Ms Clinton's election defeat to Mr Trump.
Voting in the Democratic presidential primary is not set to begin until February 2020.
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