Harvard professor Elizabeth Warren, who is seeking the Democratic Senate nod in Massachusetts, picked up the endorsement of fellow progressive former Sen. Russ Feingold (D-Wis.) on Tuesday.

“I’ve known Elizabeth … for years” Feingold wrote in an email to supporters of his Progressives United group, “and she’s exactly the type of person who should be running for office.”

“Supporting her campaign for the U.S. Senate in Massachusetts will be an absolutely crucial part of our fight against the nasty influence of corporate money in politics — and she needs all the support we can give her before Friday,” he wrote, referring to the fundraising deadline for the third quarter, which is Friday.

Warren, a former White House adviser who helped build up the Consumer Financial Protection Bureau, made her campaign against Sen. Scott Brown (R-Mass.) official earlier this month. Brown had nearly $10 million in the bank at the end of June, so Warren’s quarterly fundraising haul will be seen as a key metric of how well she’ll be able to compete against him.

Feingold, a progressive icon who served in the Senate from 1993 until 2011, lost to now-Sen. Ron Johnson (R-Wis.) by 5 points in 2010.

“In all my years in the Senate, I always took positions that I believed in, even when my own party tried to stand in the way. I know Elizabeth will be exactly the same kind of senator,” Feingold wrote.

Warren faces a crowded Democratic primary field before she has the opportunity to take on Brown.