As the crowds of protesters grow to more than 30,000, President Obama gets out in front of the Wisconsin union movement and actually takes a side - the side of workers:

President Obama thrust himself and his political operation this week into Wisconsin's broiling budget battle, mobilizing opposition Thursday to a Republican bill that would curb public-worker benefits while planning similar action in other state capitals.

Obama accused Scott Walker, the state's new Republican governor, of unleashing an "assault" on unions in pushing emergency legislation that would nullify collective-bargaining agreements that affect most public employees, including teachers.

The president's political machine worked in close coordination Thursday with state and national union officials to mobilize thousands of protesters to gather in Madison and to plan similar demonstrations in other state capitals.

Their efforts began to spread, as thousands of labor supporters turned out for a hearing in Columbus, Ohio, to protest a measure from Gov. John Kasich (R) that would cut collective-bargaining rights.

By the end of the day, Democratic Party officials were working to organize additional demonstrations in Ohio and Indiana, where an effort is underway to trim benefits for public workers. Some union activists predicted similar protests in Missouri, New Jersey and Pennsylvania.

Under Walker's plan, most public workers - excluding police, firefighters and state troopers - would have to pay half of their pension costs and at least 12 percent of their health-care costs. They would lose bargaining rights for anything other than pay. Walker, who took office last month, says the emergency measure is needed to save $300 million over the next two years to help close a $3.6 billion budget gap.

"Some of what I've heard coming out of Wisconsin, where they're just making it harder for public employees to collectively bargain generally, seems like more of an assault on unions," Obama told a Milwaukee television reporter, taking the unusual step of inviting a local station into the White House for a sit-down interview. "I think everybody's got to make some adjustments, but I think it's also important to recognize that public employees make enormous contributions to our states and our citizens."

The White House political operation, Organizing for America, got involved Monday, after Democratic National Committee Chairman Timothy M. Kaine spoke to union leaders in Madison, a party official said.

The group made phone calls, distributed messages via Twitter and Facebook, and sent e-mails to its state and national lists to try to build crowds for rallies Wednesday and Thursday, a party official said.