In this Feb. 25, 2020, file photo from left, Sen. Elizabeth Warren, Sen. Bernie Sanders, and former Vice President Joe Biden participate in a Democratic presidential primary debate in Charleston, South Carolina. Credit: Matt Rourke | AP

WASHINGTON — Elizabeth Warren endorsed Joe Biden on Wednesday, becoming the last of the former vice president’s major Democratic presidential rivals to formally back him.

The Massachusetts senator dropped out of the race last month, shortly after a disappointing third-place finish in her home state. She refused to immediately endorse Biden or her fellow progressive Bernie Sanders.

Sanders, who suspended his campaign last week, endorsed Biden on Monday, A day later, former President Barack Obama announced his public backing of Biden.