MADISON, Wis. (AP) — Embracing the label of "union boss," state firefighters president and Democratic candidate for governor Mahlon Mitchell rallied organized labor supporters Monday, urging them to unite to elect him in August and then defeat Gov. Scott Walker.

Mitchell is one of 10 Democratic candidates for governor, but his position as head of the Professional Fire Fighters of Wisconsin has given him an early advantage in union backing — both in campaign donations and people power.

Mitchell previously ran as the Democratic lieutenant governor candidate in the unsuccessful 2012 recall election against Walker. His union joined with others in marching and protesting against the Act 10 law that effectively ended collective bargaining for most public sector workers.

That law, and a host of other supported by Walker including making Wisconsin a right-to-work state, has galvanized union opposition to the Republican incumbent seeking a third term. But Democrats have been unable to defeat him and other Republicans who've supported anti-union policies, a point of deep frustration and anger that speakers at the rally Monday touched upon.

"I watched us fail in 2010," said Harold Schaitberger, general president of the International Association of Fire Fighters who came to Wisconsin to protest against Walker in 2011. "I watched us fail in 2012. I watched us fail in 2013 and 2014. When we were committed to make a change, but we didn't step up enough. We didn't bring enough to the battlefield. We didn't invest enough in order to win. This time I'm bringing everything I've got."

Schaitberger called Wisconsin "ground zero" of the national fight for middle-class workers because of Act 10. He said Mitchell was the only candidate in the crowded Democratic field who could beat Walker, who is seeking a third term after unsuccessfully running for president.

The Wisconsin Republican Party has branded Mitchell as a "union boss," criticizing his $200,000 salary in 2016 that combined his pay as a lieutenant in the Madison fire department with his $90,000 union post.

"Big labor bosses are all in when it comes to defeating Scott Walker and the reforms that have Wisconsin working," said Wisconsin Republican Party spokesman Alec Zimmerman. "Mahlon Mitchell simply embodies more of the same failed policies that put Wisconsin into a downward spiral."

Mitchell embraced the "union boss" label Monday.

"I don't mind being called that because unions helped build the best middle class in the world," Mitchell said.

Mitchell called for creating a broad coalition, with a special emphasis on black voters in Milwaukee. Mitchell, who is black, said his campaign recently opened an office on the north side of Milwaukee as part of its attempts to increase black voter turnout at the polls by as many as 50,000 voters.

"If we don't do that, we don't win a general election," Mitchell said.

The rally came hours after the liberal group Wisconsin's Choice announced that Mitchell was among four Democratic candidates that had advanced through a second round of online voting designed to pick a favorite before the Aug. 14 primary.

Wisconsin's Choice is a collaboration between the pro-Bernie Sanders group Our Wisconsin Revolution and the Wisconsin Working Families Party. It started the poll as a way to unofficially narrow the Democratic field ahead of the primary.

Along with Mitchell, others advancing to the group's final round of voting were former state Rep. Kelda Roys, of Madison, state Sen. Kathleen Vinehout and political activist Mike McCabe. The winner of the unscientific poll will be named on July 23.

Other Democratic candidates on the ballot are state Superintendent Tony Evers; state Rep. Dana Wachs, of Eau Claire; Madison Mayor Paul Soglin; Milwaukee businessman Andy Gronik; former state party leader Matt Flynn; and corporate attorney Josh Pade.

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