“Elizabeth has been listening to people across the Commonwealth as she considers a campaign,” said one Democrat operative assisting with the effort. “She wants to continue that conversation and the exploratory committee will allow her to do so. It allows her to raise money and it allows another way for people to engage with her” if they cannot see her in person.

Should Warren join the Senate race — as now seems all but certain — she faces a crowded primary field that includes Newton Mayor Setti Warren, CityYear founder Alan Khazei and activist Bob Massie. The Democratic primary is set for Sept. 18, 2012.

Many Democrats both nationally and locally see Elizabeth Warren as the likely nominee given her status as a hero of the liberal left and her presumed ability to raise money.

She’s also a lightening rod for controversy for her work in creating the Consumer Financial Protection Bureau.

Republicans in Congress have fought the new bureau tooth and nail, arguing that it will have unwarranted power over Wall Street, and they focused much of their energy on Warren herself in hearings on Capitol Hill. She left the White House last month in the face of Republican opposition to her appointment to lead the bureau.

Warren’s website, http://elizabethforma.com, contains no information beyond an email sign-up and a call for donations.

But her move closer to the race is already generating excitement among her backers.

“I’m thrilled that Elizabeth is pursuing this next endeavor with the thoughtfulness and respect that’s been such a hallmark of her career,” said Stephanie Shriock, the president of the pro-abortion rights Democratic women’s group EMILY’s List. “Elizabeth is strong, smart, and a dedicated fighter for working Americans. We’d love to see her take her talents to the U.S. Senate.”

Democrats insist that Brown is vulnerable due to the state’s heavy lean against the GOP, but he remains very popular in most polling.

An April Suffolk poll found him beating all potential Democratic challengers — although Warren was not included. A March Western New England College Polling Institute survey gave him a 53 percent approval rating. The vast majority of respondents — 59 percent — said they hadn’t heard of her; another 18 percent said they had no opinion.

Brown himself commissioned a poll that showed him with a double-digit lead over Warren.

“If she’s really listening, she’ll hear that her plans for higher taxes and more Washington spending will kill jobs,” said National Republican Senatorial Committee spokesman Brian Walsh in response, pointing out that Warren originally hails from Oklahoma.  

Massachusetts is one of ten Republican-held Senate seats on the ballot in 2012. Democrats must defend 23 seats.

More on PostPolitics

Rick Perry gets heckled in New Hampshire

Obama leaves for 10-day Vineyard vacation on Thursday

Fact Checker: Perry on climate change