Socialist Sen. Bernie Sanders is fundraising for Wisconsin Democrat Russ Feingold's campaign for the U.S. Senate.

Sanders began fundraising for Democratic National Committee Chairwoman Debbie Wasserman Schultz's primary opponent in Florida late last week, and his campaign has teased that the senator would fundraise for a dozen other candidates this week.

"When we talk about a 'political revolution,' we are not just talking about tinkering around the edges of American society. We are talking about electing candidates up and down the ballot who recognize that it is too late for establishment politics and economics in this country," Sanders wrote in a fundraising email. "That is what our campaign for president is about, and it is why I am happy to support my friend Russ Feingold's campaign for U.S. Senate."

Sanders' fundraising pitch highlighted Feingold's votes against the USA Patriot Act and the Iraq War in Congress as examples of the former senator's progressive values.

Feingold is running against incumbent Republican Sen. Ron Johnson, who defeated Feingold in 2010 amid the Tea Party wave that swept many GOP candidates into office. Early polling of the Wisconsin Senate race thus far gives Feingold the upper hand, but the race could tighten as November approaches.

Sanders' fundraising effort asks for donors to contribute $2.70, which it said it would split between Sanders campaign and Feingold.

"The final six states in the Democratic primary vote in less than two weeks and each contribution we receive, delegate we earn and state we carry sends an unmistakable message of support for the values we share," Sanders wrote. "We are working hard to win every single day, but we must also fight for change at the local level. Your contribution helps us accomplish both of those goals."