MADISON, Wis. (AP) -- Unions behind efforts that forced Wisconsin Gov. Scott Walker into a recall election are facing an uncomfortable scenario: Their favored candidate may not survive the Democratic primary now that Milwaukee's mayor is in the race.

Mayor Tom Barrett recently announced he was running to oust the Republican governor, who was targeted after championing a law that curtailed public workers' collective bargaining rights. Barrett narrowly lost to Walker in the 2010 race for governor.

Major unions are supporting Kathleen Falk, the former longtime Dane County executive.

Unions had urged Barrett not to run after he refused to promise, unlike Falk, to veto a state budget if it didn't restore collective bargaining rights.

Wisconsin police union leader Jim Palmer says Barrett is "a game changer" who would work to bring people together.