STATE HOUSE, BOSTON, FEB. 22, 2011…..As throngs of union members and their supporters crushed onto Beacon Street for a late afternoon rally in support of Wisconsin workers, the three members of the state’s Congressional delegation seen as most likely to challenge U.S. Sen. Scott Brown next year were front and center.

With a captive audience of core Democratic voters at their feet, U.S. Reps. Edward Markey, Michael Capuano and Stephen Lynch took turns rallying a pro-labor crowd, defending the collective bargaining rights of teachers, nurses, postal workers and other unionized workers.

The protest of Wisconsin Gov. Scott Walker’s proposal to eliminate core bargaining rights for unions gave the three Congressional Democrats a ready platform to reach out not just to the crowd, but to Democratic voters across the state watching the rally unfold on television and through the media.

“This is going to be a struggle at least for the next two years. Let’s be serious about this. They’re not going to back down and we’re not going to back down. This is a struggle for the hearts and minds of America,” Capuano said, referring to the Tea Party counter-protestors as a “couple of nuts in the background.”

“I’m proud to be here with people who understand that it’s more than just sending an email to get you going. Every once and awhile you need to get out on the streets and get a little bloody when necessary,” he continued.

The crowd cheered and hooted for each Congressman as they spoke - the tougher the talk, the louder the reception.

With the exception of former lieutenant governor candidate Robert Massie, who has declared his intention to run in 2012, the Democratic field for the U.S. Senate race in 2012 is wide open. Entrepreneur and social activist Alan Khazei, who founded City Year, is seriously weighing another run after finishing fourth in the Democratic primary in 2009, as is Capuano, who was the runner-up to eventual nominee Martha Coakley.

Lynch, who opted against running in 2009 when his base of labor support appeared to fracture, and Markey are also viewed as potential contenders, as is former Fidelity executive and MFS Investment Management Chairman Robert Pozen and Salem Mayor Kim Driscoll.

Brown, who already has $7.5 million in his campaign account, continues to be very popular with voters in Massachusetts, according to recent polls. This week he embarked on a book tour to promote his new memoir garnering plenty of state and national attention with interviews on 60 Minutes, The View and a full schedule of appearances and upcoming speeches across the country.

Brown has denied any direct affiliation with the Tea Party, despite their strong financial support of his candidacy a year ago, and many of the more conservative tea party members have been angered by some of his votes, including his support for repealing “Don’t Ask, Don’t Tell” and financial reform.

Still, Brown’s name was linked several times by union organizers with the Tea Party and Gov. Walker as they urged all three to “Take a walk!"

Markey, a Malden Democrat and the delegation’s senior member, blasted the Tea Party and questioned where they were when he said former President George W. Bush was running up the deficit.

“The Tea Party is defending the millionaires. The unions are defending the workers. They are not the tea party of Paul Revere and Sam Adams. They are the tea party of Alice in Wonderland,” Markey said.

Lynch, a South Boston Democrat and former local iron workers’ union president, said the core right to negotiate wages and working conditions is all unionized workers have left now that many public employees are legally prohibited from striking.

“There’s a difference between compromise and surrender, and the governor of Wisconsin wants us to surrender….,” Lynch said. “There are two visions of America here. There’s the Tea Party vision and the vision of the American worker.”

As the fight over labor rights continued in Wisconsin Tuesday, the simmering controversy over public sector compensation and benefits threatened to spill over to other states where Legislatures were weighing similar proposal to curb collective bargaining, including Ohio and Indiana.

In Wisconsin, senators took the drastic step of leaving the state for Illinois to prevent a quorum and a vote on Gov. Walker’s budget and avoid being brought back to the capitol by force by state police.

Asked whether Wisconsin Senate Democrats had an obligation as elected officials to show up and vote, Capuano argued that they were fulfilling their duty by staying away.

“They have an obligation to do their job and fight for what they believe in any way they can. That’s what the rules say. The rules require a quorum and I absolutely think they’re doing 100 percent the right thing,” Capuano told the News Service.

Some viewed the crowd-pleasing from the Congressmen as an audition before voters for a potential Senate run.

“I think they were definitely throwing some red meat out to their supporters in anticipation of future runs,” said Rep. Richard Bastien, a Gardner Republican who attended the rally.

Mary Ann Marsh, a veteran Democratic political consultant, did not hear the speeches but said, “They’ve all been great friends of labor for a very long time.”

Doug Rubin, former chief of staff and campaign advisor to Gov. Deval Patrick, echoed Marsh and said he thought it was unlikely Markey, Capuano or Lynch were looking specifically to capitalize on the moment with an eye on Brown’s Senate seat.

“It’s an important base for all of them, and an issue they all believe in so probably not,” Rubin said.