House Speaker Sara Gideon, D- Freeport, a candidate for U.S. Senate, speaks at a "Supper with Sara" campaign event at the Poulin-Turner Union Hall, in Skowhegan, Maine. Credit: Robert F. Bukaty | AP

FREEPORT, Maine — Maine House Speaker and U.S. Senate candidate Sara Gideon voted for former Vice President Joe Biden in the Democratic presidential primary on Tuesday, a spokesperson for her Senate campaign said.

Gideon is one of four Democrats competing in a primary to face off against Republican Sen. Susan Collins later this year. Two candidates, progressive lobbyist Betsy Sweet and lawyer Bre Kidman, endorsed Vermont Sen. Bernie Sanders prior to the election, while the other two, Gideon and former Google executive Ross LaJeunesse, declined to endorse.

Gideon said on Tuesday she sees Biden as the candidate “most able to bring the country together and to look into the future to address all the challenges we face.”

Collins, who did not support President Donald Trump in 2016, has declined to say whether she voted for him in the Republican primary this year, when he was the only candidate on the ballot.

Maine’s U.S. Senate race is expected to be one of the most competitive in the nation, with a Colby College poll in mid-February showing Gideon and Collins virtually tied in a hypothetical general election match up.

Several independents, including Trump-supporting conservative Max Linn, former 2nd Congressional District candidate Tiffany Bond and former Green hopeful Lisa Savage, are also trying to make the November ballot.