The Massachusetts senator sent out an appeal Thursday on behalf of Merkley, who is up for reelection in 2014. Merkley seems like a safe bet for reelection.
However, Warren's appeal is significant because it marks new financial and political aid that progressive senators have not previously enjoyed. Warren formed a political action committee, PAC for a Level Playing Field, late last year and solicited donations for it earlier this month.
Warren's 2012 candidacy excited progressives and she raised a whopping $42 million -- more than any other candidate during the cycle. Her email to supporters could lend some of that excitement to Merkley.