In the race for governor in Massachusetts, the bully card is being tossed around.

Democratic candidate Shannon O'Brien says Republican rival Mitt Romney and his supporters have crossed the line by associating her with corporate scandal. A Romney spokesman responded in kind, calling O'Brien "the bully in the race.''

The issue raises a delicate question for Romney or any of O'Brien's three male Democratic primary opponents — former U.S. Labor Secretary Robert Reich, state Senate President Tom Birmingham, and former state Sen. Warren Tolman: How aggressively should they go after a woman?

Campaigning is sure to become more intense, with polls showing O'Brien leading and the Sept. 17 primary only three weeks away. The Massachusetts race has been one of the more closely watched campaigns in a year when 36 states are deciding gubernatorial elections.

"It's awfully tough for a man to know how to treat a female opponent,'' said Ralph Whitehead, a University of Massachusetts journalism professor. "If the male candidate holds back, he might miss an opportunity to press his case, but if he comes on strong, he might look overbearing or even a bully.''

O'Brien, the state treasurer, said Romney's supporters went too far last week by showing her photo next to disgraced Enron Corp. and WorldCom Inc. executives and holding signs that accuse her and her husband, former Enron lobbyist Emmet Hayes, of "corruption and lies.''

"I think Mitt Romney is afraid of me,'' O'Brien said this week. "Ultimately bullies are afraid, and that's why he's acting this way.''

Romney spokesman Eric Fehrnstrom said the state Republican Party is acting appropriately by questioning O'Brien's record as state treasurer.

"There is no crying in politics,'' Fehrnstrom said.

O'Brien said she was nearly knocked over trying to enter a campaign event in Boston last week by Republican protesters who heckled her and held signs. One said, "Shannon stole my pension money.'' Another said, "Shannon plus Emmet equals corruption and lies.'' Romney, the former Salt Lake City Olympics chief, did not attend.

Once inside, O'Brien referred to Romney as a "bully,'' then repeated the charge two days later.

The state Republican Party last week launched a radio advertisement that assails O'Brien for her record.

O'Brien said it's fine to question how the state pension fund has been invested on her watch, but, "It's another thing altogether to slander me, to say that I stole money, and to call my ethics into question.

"I think that's stepping over a line,'' she said.

The bully issue is particularly sensitive for Romney, whose imminent entry into the governor's race forced acting Gov. Jane Swift, a fellow Republican, to tearfully announce her withdrawal in April. Opponents accused Romney of "elbowing'' aside Swift.

Fehrnstrom, the Romney spokesman, said there's plenty of "bully'' blame to go around. O'Brien and her Democratic Party acted as bullies, Fehrnstrom said, by challenging Romney's residency and trying to keep him off the ballot.

"Shannon O'Brien is the bully in the race,'' Fehrnstrom said.

It's not the first time the bully card has been played.

The issue became a key turning point in Hillary Clinton's 2000 U.S. Senate race in New York. In a debate, her opponent Rick Lazio crossed the stage and waved a document in her face as a television audience looked on.

Clinton's campaign used the encounter to portray Lazio as a bully, calling him "menacing'' and comparing him to Bobby Knight, the basketball coach known for hurling a chair onto the court. Clinton eventually won.

Massachusetts has never elected a woman governor. Swift, the lieutenant governor, was the first woman to move into the office last year when Paul Cellucci became U.S. ambassador to Canada.

Larry Sabato, a University of Virginia political scientist, said it's difficult enough for women to convince voters they can stand up to male politicians, especially in executive positions such as governor or president.

O'Brien's complaints may exacerbate those doubts, he said.

"It's sexist but most Americans think that women are not up to the rough and tumble of politics,'' Sabato said. "This may not be a wise move for her. It suggests she's overly sensitive to the rough and tumble of politics.''