Sanders won the caucus due to large voter turnout across the state, defeating Clinton by a 2-to-1 margin. According to local news reports, voters waited in long lines to participate in the caucus.

His win in Maine, along with wins in Kansas and Nebraska on Saturday, buoyed the spirits of his supporters and are encouraging signs for his campaign. But Sanders continues to trail Clinton in state-level victories and delegates, and faces an uphill battle in trying to close the gap.

On Sunday, Sanders and Clinton participated in a debate in Flint, Michigan, ahead of the state's primary on Tuesday. Both candidates are looking for a victory in the delegate-rich state, with Sanders hoping that his platform of fighting income inequality resonates with Michigan voters, who have faced a disproportionate amount of economic upheaval.

From there, the Democratic presidential race moves to Florida, Illinois, Missouri, North Carolina and Ohio on March 15. These contests favor Clinton, given that Sanders has done better in smaller, more predominantly white states, while Clinton has done better in bigger, more diverse states.