But where Senator Brown sees an objectionable tactic motivated by crass political calculations, backers of the move in Massachusetts say it's simply an effort to comply with federal law.
What both sides agree on is this: Under pressure from a lawsuit with liberal backers, the state government has agreed to send voter registration forms to anyone on the state's welfare rolls during the past year, or about 478,000 people.
"I want every legal vote to count, but it's outrageous to use taxpayer dollars to register welfare recipients as part of a special effort to boost one political party over another," Brown said in a statement released Wednesday. "This effort to sign up welfare recipients is being aided by Elizabeth Warren's daughter and it's clearly designed to benefit her mother's political campaign."
The political advocacy group Demos, which helped file the lawsuit against Massachusetts, quickly fired back, calling the issue nonpartisan: "It is fundamental to our democracy that all eligible citizens be accorded the maximum opportunity to register and vote," said Miles Rapoport, the group's president. "We completely reject the Brown campaign’s or anyone else's assertion that this is politically motivated or coordinated in any way."
This may be one of those shouting matches where what's credible depends on the ideological eye of the beholder, but it also has substantive meaning for the campaign. This Senate race appears to be so close that even modest changes in voter participation and turnout could affect the outcome.
In several recent polls, Brown is essentially tied with Warren, a Harvard professor who gained national stature for her watchdog role on a congressional panel on the financial crisis and bailouts for Wall Street banks. Come November, the decisive factor could be which side is more effective at mobilizing its sympathizers into the voting booth.
Citing recent news reports, the Brown campaign says the state has sent voter registration letters to nearly 500,000 welfare recipients. The campaign is also pointing out that Elizabeth Warren's daughter, Amelia Warren Tyagi, chairs the Demos board of trustees.
Mr. Rapoport of Demos, in his statement Wednesday, said Ms. Tyagi did not encourage any work aimed at benefiting her mother's campaign. Demos was promoting enforcement of the 1993 National Voter Registration Act "well before Amelia came on our board, and we are going to continue it long after this year's election is over," he said.
The 1993 act, often known as the motor-voter law, was designed to boost voter participation by requiring states to offer registration when residents apply for driver's licenses or social services. It was passed when the Democrats controlled both Congress and the White House. Since the law went into effect in 1995, the nation has seen little change in the overall level of voter registration.
Demos says it has worked state by state since 2004, partnering with local groups to pursue stronger enforcement of the federal law. The lawsuit in Massachusetts was filed in May 2012, as the Brown-Warren race already appeared likely to be one of the hottest Senate races nationwide.
By July 5, the plaintiffs and the state reached an interim agreement in which the state committed to mail registration papers to welfare recipients in time for November elections. Demos says the parties will continue to negotiate a long-term agreement, and that the lawsuit could resume if there is no final settlement agreement by the end of December.
According to census data, the share of Massachusetts residents who are registered voters differs little from the national average. Some 72.6 percent of the state's US citizens over 18 were registered as of the 2008 election, compared with 71 percent nationwide. Most of the state's New England peers have higher registration levels, however.
Demos, citing census data, says that only 58 percent of the commonwealth’s eligible low-income citizens were registered to vote, compared with 77 percent of higher-income citizens, and that the number of voter registration applications reported by public assistance offices has "plummeted" over the past 10 years.