(CNN) — Elizabeth Warren is expected to endorse presumptive Democratic presidential nominee Hillary Clinton Thursday, according to a source close to the Massachusetts senator.
Warren, a liberal stalwart known for championing issues related to economic inequality, has been one of the few Democratic senators to withhold a formal presidential endorsement.
She was already set to deliver a blistering critique of Donald Trump on Thursday at a speech in Washington, continuing her recent role as antagonist to the presumptive Republican presidential nominee.
Warren wanted to speak to Sen. Bernie Sanders, Clinton’s primary rival, first, which is expected to happen later Thursday, most likely by phone.
The source said the decision was made to do it Thursday, on the heels of President Barack Obama’s endorsement, “to make it more forceful for the overall goal.”
Warren’s endorsement is expected to come in an interview with MSNBC’s Rachel Maddow.