Wis. Democrat launches formal challenge to Walker

But Milwaukee Mayor Tom Barrett, a Democrat who lost to Walker in 2010 by 6 points, is thinking about joining the race even though union leaders have privately discouraged him. Barrett has clashed with unions over decisions he's made as mayor. Marty Beil, the head of the largest state workers union, has spoken out against Barrett and said the candidate needs to be someone who is a labor champion.

Barrett's campaign spokesman Patrick Guarasci said Barrett has deep, statewide support and was considering running. He is also seeking re-election as mayor, which will be decided on April 3.

Unions have had a mixed record of late. Republicans saw huge victories in 2010, winning majorities in both the state Senate and Assembly, despite union opposition. Last summer, organized labor was heavily involved and spent millions on behalf of Democrats who were running in six recall elections targeting Republicans. Only two Democrats won.

But Walker's opponents say the recall drive shows that voters are energized. The 1 million signatures organizers say they collected against him equates to about 47 percent of the number of people who voted in the 2010 governor's race.

Walker, who was in New York City on Tuesday and Wednesday to raise money, said he will prevail because voters will choose his vision for the future over what he called the failed policies of Democrats.

A number of other Democrats are still considering a run, and others hope retiring U.S. Sen. Herb Kohl will change his mind and get into the race. At least for now, the 76-year-old Kohl is unmoved.

Walker said it didn't matter to him who his challenger was because he views his opponent as "big money from out of state from public employee unions."

"In the end, I'm less worried about who the opponent is than I am about defending my record," Walker said.