Vermont Sen. Bernie Sanders to announce 2016 presidential run

(J. Scott Applewhite/AP)

Sen. Bernie Sanders, I-Vermont, is planning to announce on Thursday that he will run for president in 2016 and will enter primary and caucus contests as a Democrat, a senior Sanders adviser told ABC News.

The announcement will indicate that Sanders will launch his campaign in May, most likely in his home state of Vermont.

Sanders’ entry in the race gives Democrats at least one liberal alternative to former Secretary of State Hillary Clinton, who declared her candidacy earlier this month. Sanders will also be Clinton’s first formal Democratic challenger.

Sanders is a self-described independent socialist and will enter the race as a definite long shot.

The expected announcement comes at a time of growing liberal unease over President Obama’s agenda and amid angst that Clinton won’t be pushed sufficiently leftward with Sen. Elizabeth Warren, D-Massachusetts, taking a pass on the race.

Sanders, 73, currently serves as the ranking member of the Senate Budget Committee and previously served as the chairman of the Senate Committee on Veterans’ Affairs. Sanders has proudly noted he’s the longest-serving independent member of Congress in U.S. history.

ABC News’ Arlette Saenz contributed to this report.

(Cover tile photo: Win McNamee/Getty)

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