Massachusetts senator Elizabeth Warren dropped out of the Democratic presidential primary on Thursday, joining former South Bend mayor Pete Buttigieg and Minnesota senator Amy Klobuchar as recent exits from the race.

Buttigieg and Klobuchar rapidly endorsed former Vice President Joe Biden and apparently inspired their supporters to fall in line, with Biden’s victories in ten states on Super Tuesday clearly buoyed by a consolidated moderate front. Warren has the capacity to reverse the centrists’ momentum. For the project of progressive change to have a fighting chance, she should immediately endorse Bernie Sanders — and urge her supporters to back the Vermont senator as well.

One of the most progressive Democrats in the Senate, Elizabeth Warren entered the political arena in the early aughts by picking a fight with Sanders’s sole remaining viable opponent. Joe Biden allied with credit card companies and Senate Republicans behind a bill to tighten eligibility requirements for personal bankruptcy, a move the then-law professor and consumer rights advocate fiercely opposed. This fight would become a crucial piece of Warren’s political origin story — she’s cited it as the episode that whet her appetite for an uphill populist fight, as well as what educated her about monied interests’ chokehold on the political system.