Former U.S. Senator Russ Feingold, Democrat from Wisconsin, on Thursday announced plans to run for reelection and regain the seat, setting up a rematch with Republican Ron Johnson, whom Politico describes as "one of the most vulnerable incumbents on the 2016 Senate map."

Feingold represented Wisconsin in the U.S. Senate for 18 years before he was defeated by the conservative Johnson in 2010's "Tea Party wave." However, as Politico points out, Feingold appears to have an advantage even two years ahead of the election, with a Marquette Law School poll conducted last month giving him 54 percent of the vote.

In a video announcing his run, Feingold singled out money in politics as a major factor in his campaign.

"People tell me all the time that our politics in Washington are broken and that multi-millionaires, billionaires and big corporations are calling all the shots," he stated. "They especially say this about the U.S. Senate, and it's hard not to agree."

The Senate needs "strong independence, bipartisanship, and honesty," Feingold said.

While in the Senate, Feingold "was the Democrats' leading campaign finance scold—and he "lived up to his principles in practice," writes National Journal political editor Josh Kraushaar. "He refused any outside spending from the Democratic Senatorial Campaign Committee in his unsuccessful 2010 campaign, and from any other outside super PACs... Feingold is a favorite of progressives, and his candidacy would be a reliable way to energize the grassroots base."

His announcement is seen as a solid development for the progressive wing of his party. Grabbing an endorsement from the Democratic Senatorial Campaign Committee almost immediately, DSCC chairman Jon Tester called Feingold "a tenacious champion for the people of Wisconsin throughout his career."

In an email heralding Feingold's announcement, the Progressive Change Campaign Committee said that should the former senator win, "Elizabeth Warren will have another bold ally by her side."