Sen. Elizabeth Warren Elizabeth Ann WarrenWoman to undecided Biden: 'Just say yes' to 2020 bid Raising taxes on the wealthy is 'extremely popular,' says Dem pollster 64 percent say Democratic Party supports socialism, says poll MORE (D-Mass.) will endorse presumptive Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonREAD: Cohen testimony alleges Trump knew Stone talked with WikiLeaks about DNC emails County GOP in Minnesota shares image comparing Sanders to Hitler Holder: 'Time to make the Electoral College a vestige of the past' MORE in a Thursday TV appearance.

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Warren will announce her support for Clinton on MSNBC's "The Rachel Maddow Show" at 9 p.m., the network confirmed.

Warren has so far remained neutral during Clinton's heated Democratic presidential primary against Bernie Sanders Bernard (Bernie) SandersSenate Dems seek to turn tables on GOP in climate change fight Bernie Sanders Town Hall finishes third in cable news race, draws 1.4 million viewers Woman to undecided Biden: 'Just say yes' to 2020 bid MORE, but her endorsement could ease progressive voters who are reluctant to get behind Clinton and unify the Democratic Party heading into the general election.