CALL IT THE CURSE of the front-runner. Opinion polls consistently show Treasurer Shannon O’Brien leading the five Democrats running for governor. But her campaign appears somewhat unfocused, hesitant, and inconsistent. One moment, it’s rolling out a transparent proposal calling on her opponents to pledge against running negative campaigns — widely seen as an effort by O’Brien to evade questions about her husband Emmet Hayes, who used to lobby for Enron. The next, it’s scrambling to defend O’Brien against charges from gubernatorial candidate and Senate president Tom Birmingham that she never supported an income-tax rollback with economic triggers (i.e., the performance of the economy determines the extent of the tax cut).

None of this is to suggest that O’Brien lacks star power. On the contrary: this past Saturday, for instance, O’Brien drew 150 Democratic women activists to a two-hour "Conversation with Shannon O’Brien" held at the First Baptist Church in Waltham — not an easy feat on the first brilliant Saturday of the spring. O’Brien delivered a town-meeting performance that would have done President Bill Clinton proud. She opened with a joke prompted by an embarrassing misstep on the day before. (The background: on Friday, at a breakfast forum at which the five Democratic candidates appeared, her rival Steve Grossman made the point that his opponents could not even spell the word "accountability." Intending to one-up him, O’Brien decided to respond by spelling out the word; unfortunately, however, she spelled it "accountability" — missing the second i — a gaffe noted by the Associated Press and the Boston Herald.) "I’m embarrassed because I’m a good speller," O’Brien told the crowd, noting that she’d been a high-school cheerleader. "Not a public-school cheerleader — a Catholic-school cheerleader," she said, setting up the punch line. "Try doing a split and spelling ‘Immaculate Conception,’ " she finished, to howls of laughter.

The rest of her talk built on the momentum of her opening. Audience members asked questions on a wide array of topics, including the possibility of restoring state aid to cities and towns, the foster-parent system, higher education, gay civil unions, and care for elderly parents. On local aid, she reminded the audience that "we only have one set of taxpayers" and took a veiled shot at Republican nominee Mitt Romney, who only recently returned from Utah, where he ran the Winter Olympics: "Wouldn’t it be nice to ask the people of Utah to pay for our water and sewer programs?" On health care, she mentioned that she’s working on a health-care-policy plan with former state legislator John McDonough, now a Brandeis professor: "The administration must be working with these health-care entities to make sure more people get access to health care." On care for elderly parents, O’Brien said that the income-tax rollback advocated in 2000 by then-governor Paul Cellucci and currently supported by Romney has constrained Beacon Hill’s options: "Mitt Romney is loyal to a tax cut, not to the families who have to care for older parents."

There’s no question that O’Brien’s talk was a winner. Afterward, Arlington Democratic activist Roberta Selleck said O’Brien did well enough to win Selleck’s support away from former secretary of labor Robert Reich. "With Mitt Romney in the race, we need somebody who is politically much stronger and politically much better rooted in Massachusetts," Selleck said. O’Brien’s aides hope that they can transform such audiences of activists into grassroots supporters.

Just three weeks before the Democratic Convention in Worcester, however, O’Brien’s performance raises more questions about her campaign than it answers. Why wasn’t a video crew on hand to tape her appearance for use in political ads? More important, why hasn’t the public seen more of this smooth, strong O’Brien? Only days earlier, for example, she gave an uptight, somewhat muted speech at the launch of her economic-development plan in Newton. And when Democrats debated at the Kennedy Library on April 1, O’Brien’s execution was uninspired; even the charisma-impaired Tom Birmingham appeared to outshine her.

These missteps seem to be the product of a conservative political campaign that would rather keep O’Brien under wraps than let her loose. It seems content to have O’Brien coast as the Democratic front-runner (recent polls put her at 29 percent among Democrats, six points ahead of her closest Democratic rival, Robert Reich), while cultivating the support of convention delegates behind the scenes. In the meantime, O’Brien prefers to hoard her $2 million in campaign funds rather than spend on high-profile television ads that could extend her lead in the polls. She seems, in some ways, to be a victim of the front-runners’ curse: afraid to do anything lest it destroy her position. O’Brien’s strategy — which seems to hinge on waiting to fight it out in August — might win the Democratic nomination. But in the general election, will it be enough to defeat a telegenic and well-known Republican opponent like Mitt Romney — a candidate who spent $8 million in his last statewide race in Massachusetts?