From left, Democratic presidential candidates Sen. Bernie Sanders, I-Vt., and former Vice President Joe Biden, participate in a Democratic presidential primary debate at the Gaillard Center, Tuesday, Feb. 25, 2020, in Charleston, S.C., co-hosted by CBS News and the Congressional Black Caucus Institute. Credit: Patrick Semansky | AP

AUGUSTA, Maine — Vermont Sen. Bernie Sanders has picked up more progressive backers in Maine, while former Vice President Joe Biden benefited from late-breaking dropouts Monday, a day before Maine and 13 other states will vote in the Democratic presidential primary.

Biden might be picking up support in Maine after three candidates — former Mayor Pete Buttigieg, Minnesota Sen. Amy Klobuchar and billionaire Tom Steyer — dropped in the final three days before the Democratic presidential primary in Maine. Massachusetts Sen. Elizabeth Warren still has the most endorsements from state-level officials in Maine.

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Klobuchar’s campaign confirmed Monday afternoon that she would drop out and support former Vice President Joe Biden. Former Mayor Pete Buttigieg of South Bend, Indiana, who polled in second place behind Sanders in Maine just a few weeks ago, announced Sunday that he was dropping out. Billionaire activist Tom Steyer dropped out on Saturday.

Her announcement that she would drop out of the race came just after she made a Saturday campaign stop in Portland. Her campaign had also announced nine endorsements in Maine on Monday morning. One of those endorsers, Bangor City Councilor Ben Sprague, said he would now support Biden. Two of Buttigieg’s past endorsers, State Treasurer Henry Beck and State Rep. Andrew McLean, D-Gorham, both said Monday that they would support Biden.

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With Buttigieg and Klobuchar out, Sanders and Biden have emerged as the two frontrunners nationally. Sanders, who led in a Colby College poll of Maine released in mid-February, picked up another round of endorsements of his own this weekend, bringing him to nearly a dozen endorsements from state legislators.

U.S. Senate candidate Betsy Sweet, one of four Democrats competing in a June primary, also endorsed Sanders on Sunday, calling the Vermont senator “the first voice in many forward-thinking movements for change.” Sweet is the second U.S. Senate candidate to endorse Sanders, following Saco lawyer Bre Kidman.

Former New York City Mayor Mike Bloomberg has yet to compete in a primary contest and remains a wild card in Maine. He racked up a lengthy list of endorsements in the state, including former U.S. Reps. Mike Michaud of the 2nd District and Tom Allen of the 1st District.

Bloomberg’s campaign said it used the final weekend before the Maine primary to make an organizing push. Crystal Canney, Bloomberg’s state director, said the campaign knocked on 21,000 doors over the final week and made contact with 6,500 voters in person or by phone.

The Maine primary is highly uncertain, since seven of the 12 candidates who qualified for the ballot have now dropped out of the race. Their exits could allow Biden, Bloomberg and Warren to join Sanders in reaching a 15 percent threshold needed to win a share of delegates to the Democratic national convention, though votes for the candidates who left the race will count.