Maine Democrats held 533 caucuses at approximately 400 locations across the state, and 30 delegates are at stake.
On Saturday, Sanders won the Kansas and Nebraska caucuses while rival Hillary Clinton took the Louisiana primary.
Despite winning two states, the delegate math doesn't favor the Vermont senator. Clinton actually won more delegates on Saturday than Sanders -- 65 to 47 -- and leads him overall 1,121 to 479, which includes pledged and superdelegates.
Sanders said Sunday on ABC's "This Week with George Stephanopoulos" that "we have a path toward victory" signaling, at least for now, that he is in the race for the long haul.
"We think we have an excellent chance to do well out on the West Coast in California, state of Washington, Oregon," he said. "We think we have an excellent chance to do well in large states like New York. We think we're going to surprise people here in Michigan."
ABC's Josh Haskell contributed reporting.