(CNN) - Populist darling Elizabeth Warren, along with the Progressive Change Campaign Committee, threw their support Thursday behind Bruce Braley in the race for an open U.S. Senate seat in Iowa.
Braley, a four-term congressman is hoping to keep the seat longtime Democratic Sen. Tom Harkin, who's retiring at the end of this year, in party hands.
The endorsement comes after Braley drew fire earlier this week for dismissing six-term Iowa GOP Sen. Charles Grassley as "a farmer from Iowa who never went to law school."
Braley later apologized and his campaign quickly shot out a series of releases touting the candidate's rural Iowa background.
Warren, a freshman senator from Massachusetts, and the progressive group also announced they are backing Rick Weiland in his candidacy for an open U.S. Senate seat in South Dakota.
"Two of my Democratic colleagues in the Senate, Tom Harkin of Iowa and Tim Johnson of South Dakota, are retiring this year. Karl Rove and the Koch Brothers are already spending huge amounts of money to pick up those seats," Warren said in a release.
Weiland, the only Democrat in the race, threw his hat in the ring after Democratic Sen. Tim Johnson announced last year he would not seek reelection.
Weiland may likely face Republican Gov. Mike Rounds, the frontrunner on the GOP side.
Johnson's announcement and a string of other Senate Democratic retirements have further stoked Republican hopes of picking up enough Senate seats in November's midterm election to force Democrats in the minority in the upper chamber.
Republicans need to pick up six seats to win the majority.
CNN's Dana Davidsen and Paul Steinhauser contributed to this report.