For the Democrats, an initial wide field of prospective candidates narrowed after the entry of Harvard Law School professor Elizabeth Warren, the architect of the Consumer Financial Protection Bureau.

Opinion polling indicated a close race for much of the campaign, though Warren opened up a small but consistent lead in the final few weeks.

Despite his loss, Brown received 8.6% more of the state vote than Republican former governor of Massachusetts Mitt Romney did in the concurrent presidential election.

[3] The Massachusetts Republican Party sued in an attempt to halt Kirk's appointment, but it was rejected by Suffolk Superior Court Judge Thomas Connolly.

[5] Brown thus became the first Republican to be elected from Massachusetts to the United States Senate since Edward Brooke in 1972, and he began serving the remainder of Kennedy's term on February 4, 2010.

[6][7] The National Republican Trust PAC, a group integral to Brown's 2010 election, vowed to draft a conservative opponent, citing dissatisfaction with his vote in support of the New START nuclear arms treaty.

[12] As the only candidate with 15% of delegate votes necessary to qualify for the primary ballot, Warren eliminated her challenger Marisa DeFranco, becoming the de facto nominee.

[13] On September 14, 2011, Warren declared her intention to run for the Democratic nomination for the 2012 election in Massachusetts for the United States Senate.

[42] Warren and her opponent Scott Brown agreed to engage in four televised debates, including one with a consortium of media outlets in Springfield and one on WBZ-TV in Boston.

Warren criticized Brown for continually voting with Republican leadership, and argued that he was not the bipartisan moderate he claimed to be.

Warren said that Wall Street CEOs "wrecked our economy and destroyed millions of jobs" and that they "still strut around congress, no shame, demanding favors, and acting like we should thank them.

According to Brown, he had rejected an offer to play a larger role, and limited his attendance to a single day because of scheduling demands.

But part of the underlying social contract is, you take a hunk of that and pay forward for the next kid who comes along.On July 13, 2012, President Obama sparked a controversy when he echoed her thoughts[62][63] in a campaign speech saying, "Somebody helped to create this unbelievable American system that we have that allowed you to thrive.

In August 2012, Rob Engstrom, political director for the United States Chamber of Commerce, claimed that "no other candidate in 2012 represents a greater threat to free enterprise than Professor Warren.

[67] In April 2012, the Boston Herald sparked an election controversy when it drew attention to Warren's Association of American Law Schools (AALS) directory entries from 1986 to 1995, which listed her as a minority professor.

[68] According to the AALS, the directory was compiled by information supplied by law school deans, based on questionnaires filled out by individual teachers.

[70] Harvard Law School had listed her as a minority professor in response to criticisms about a lack of faculty diversity, but Warren said that she was unaware of this until she read about it in a newspaper during the 2012 election.

[72][73][74] In response, Warren's brothers issued a joint statement stating that they "grew up listening to our mother and grandmother and other relatives talk about our family's Cherokee and Delaware heritage".

[81][82] Former colleagues and supervisors at the universities where she had worked (including Charles Fried, former Solicitor General under President Ronald Reagan) said Warren's ancestry was either not mentioned, or played no role in her hiring.

The candidates agreed to a fourth debate which was to be held on October 30 in WGBH-TV's studio, hosted by a Boston mediaB consortium, and moderated by John King, but the day before both pulled out due to Hurricane Sandy.

[225][226] Both Warren and Brown stated early in the race that they would not accept television advertisement assistance from Super PACs and interest groups.

As expected, Warren performed very well in Suffolk County, which is home to the state's largest city and its capital Boston.