It could be the race of the liberal firebrand against the Republican savior:  Elizabeth Warren, who angered both Republicans and Democrats as a consumer advocate, is inching toward a run for the U.S. Senate in Massachusetts, where she’d face off against Sen. Scott Brown, the Republican who shocked the political establishment by winning the seat Democrat Ted Kennedy held for more than four decades.

Warren headlined a packed labor event in Boston Monday, and has been raising campaign money and assembling volunteers to work for her should she declare her candidacy.

The Harvard Law professor, who made a national name for herself as a government watchdog and consumer advocate, stayed coy about whether she would enter the Democratic primary when she addressed the Greater Boston Labor Council at its annual Labor Day breakfast. But as soon as she mentioned a potential run, she was interrupted by thunderous applause.

“I’m not giving up without a fight. I’m going to keep fighting for middle-class families, for working people, whether I fight as an outsider or I fight from the floor of the Senate,” Warren told those assembled. Those words were met with a standing ovation.  “I will continue to stand for you,” she continued. “This is a big fight — the biggest fight of our lifetimes – and we will throw everything we’ve got into it.”

Warren helped create the Consumer Financial Bureau but was passed over to lead it mostly because of Republican opposition. This summer she has been on a listening tour of Massachusetts, meeting with supporters.  On Monday she previewed the themes a Warren campaign.  She talked about her childhood lived on the “ragged edge of the middle class,” and said she knew the “anxiety that comes with living one pink slip or one serious medical problem away from financial collapse.” 

Not yet a candidate but a headliner at the Labor Day event , Warren did get to sit on the dais while her potential Democratic rivals were relegated to working the room from the floor, according to the Boston Globe. It might have looked like a labor endorsement for Warren, but  she  is not in the race yet and with six potential Democratic rivals, there will be an intense primary battle, despite what now looks like  establishment Democratic support in the state.

In the meantime,  her supporters are moving ahead and holding house parties to try to convince their friends and neighbors to support Warren now.

Warren’s support is not only in Massachusetts. The Progressive Change Campaign Committee raised more than $105,000 for a Draft Warren effort, and according to PCCC, almost another $10,000 has been donated to Warren’s exploratory committee.

 Cynthia Curtis was put in touch with three other Warren supporters, and in a week, set up a “Draft Warren” house party in her Wellesley home for more than 50 people, many of whom she didn’t know.

“The enthusiasm was electrifying. Everybody knew she wasn’t going to be there. It’s not something affiliated with her exploratory committee and all these people came,” Curtis said.  “I think she will immediately leap to the head of the pack and certainly hearing from folks in attendance last week, there’s not an awful lot of enthusiasm for the other candidates. … She’s a fighter, she’s a believer in equality, she’s a believer in fairness. She’s a believer and supporter of the middle class, and I think that’s really lacking today.”

Curtis said  she’s a registered independent, and even voted for Brown when he ran for the Massachusetts State Senate, because she lived in his district, but said she didn’t “know what Scott Brown stands for anymore.”

“I think, unfortunately, he’s become very much blowing in the wind. There is nothing I know he stands for other than supporting the troops, which is great.”

Although Warren seems ready to take on Brown, she has to first withstand the primary.  She could face City Year co-founder Alan Khazei; Newton Mayor Setti Warren;  State Rep. Thomas Conroy;  Bob Massie, who is a former candidate for lieutenant governor; immigration attorney Marisa DeFranco; and engineer herb Robinson from Newton — all declared candidates.

Kevin Franck, a spokesman for the Massachusetts Democratic Party, told ABC News it was  not “encouraging anyone” nor “discouraging anyone” from jumping in.

“We would certainly welcome Warren into the race. She brings a lot of enthusiasm. A lot of Democrats are very eager to see her as a candidate,” said Franck. “Elizabeth Warren has been talking to the grassroots, doing the hard work that needs to be done to set the stage for a campaign, and that’s what she needs to do if that’s what she decides.”

But Franck predicted that even during the primary, the “focus will stay on Scott Brown throughout.”

“Although it will be hotly contested, I don’t think they [Democratic candidates] will hit each other. Instead, they will be focused on telling the people of Massachusetts that Brown is not representing them well and forcing the senator to defend his record at every turn up until Election Day,” Franck said.

Brown surprised the country by defeating State Attorney General Martha Coakley in deep blue Massachusetts last year. He’s sure to return to themes from that campaign in which  he drove around the state in his pickup truck focusing on connecting to independent Massachusetts voters with his story of overcoming a hardscrabble, difficult childhood, and  pledging to work across the aisle.

The Brown campaign said it is “under no illusions that this will be easy,” because Brown is a Republican in Democratic Massachusetts. But Brown, his campaign emphasizes, is “willing to work across party lines”  and is an “independent thinker” as it tries to paint Warren as an out-of-touch elitist.

“Elizabeth Warren has spent her adult life on the campus of Harvard,” a Brown aide said. “She’s never been a part of the real world. I think that the more and more we see and hear from her, we’ll see her views as a Harvard professor, less the streets of Southie and the commonsense views that voters saw in Sen. Brown.  It’s like William F. Buckley said, ‘I’d rather be governed by the first 2,000 names in the Boston telephone directory than by the 2,000 members of the Harvard faculty.’ I think the people of Massachusetts agree with that very much.”

Brown campaign manager Jim Barnett told ABC News that the junior senator from Massachusetts “has been fighting for commonsense, bipartisan solutions to put people back to work and get our economy back on track.”

Warren’s spokesman Kyle Sullivan highlights Warren’s personal struggles.  “She is taking some time to decide whether to run … listening to people across the commonwealth.  Like a lot of people in Massachusetts, Elizabeth is frustrated with Washington because it’s not working for middle-class families. She knows the struggle people are facing, because she grew up facing those struggles too. It’s why Elizabeth has made fighting for middle class families the work of her life,” Sullivan told ABC News.

 The grassroots may be gearing up for Warren, but the Massachusetts Republicans are quick to point out that there is a primary to contend with, and even if she does get in, it may not be pretty.  

 ”The Democrats have a long primary ahead of them, one that could be rather divisive and rather expensive,”  said Tim Buckley, communications for the Massachusetts Republican Party. “This election is going to be all about jobs and the economy. It’s going to be about getting people back to work and Scott will continue to work hard for regular people back here in Massachusetts. He’s kept the promise he made in 2010 to be an independent voice and he will continue to do that. Massachusetts voters know this now and will likely not forget that in the ballot booth in November.”

 Yet this doesn’t dim the enthusiasm of  early Warren supporters like Cynthia  Curtis, who said  she can’t wait until Warren makes it official.

 ”I wish she would hurry up and announce,” Curtis said. “There will be a lot of disappointed folks if she decides not to run. There’s a tremendous amount of enthusiasm, and this enthusiasm did not exist for Martha Coakley.”