LOWELL — The second debate between Senator Scott Brown and Democrat challenger Elizabeth Warren featured a lot of friction but not much new illumination, lacking a game-changing moment even if it was marked by two stumbles that illustrate lingering challenges for each candidate.

For Brown, the Republican incumbent, it came when his careful efforts to modulate his apparent dislike for Warren slipped and he asked her to stop interrupting.

“Excuse me, I’m not a student in your classroom,’’ he told the Harvard Law School professor.

The tartness stirred boos from Warren supporters in the crowd of some 5,700 at the University of Massachusetts Lowell’s Tsongas Center, a huge audience that gave Brown and Warren the aura of gladiators as they squared off on the arena floor.


It also was unlikely to wear well with viewers of their first debate on Sept. 20, many of whom remarked that Brown was too hot-headed in that encounter. Both occasions have fueled questions about Brown’s true temperament, and whether his carefully honed nice-guy, everyman image is just that, an image.

Yet Warren raised questions about her own authenticity, although not in response to another series of opening questions about her Native American heritage.

She countered them with perhaps her best explanation yet of the campaign, saying, at root, the issue is not whether she has a character flaw, as Brown has suggested. He has accused her of using unjustified claims of minority status to advance her academic career.

“You know, I think character is how you live your life,’’ Warren told moderator David Gregory, host of NBC’s “Meet the Press.’’

“I am the daughter of a janitor who ended up as a professor at Harvard Law School and working for the president of the United States,’’ she said. “I have taught school, I have taught generations of students, and I hope occasionally inspired a few of them. And I have worked hard for 30 years to make the legal system just a little bit fairer for people.’’


When Gregory pressed her for regrets, Warren said: “You know, I wish I had been faster in answering the question. But the truth is the truth.’’

For Warren, though, her authenticity as a candidate — or at the very least, her articulateness — was drawn into question when she was asked to rebut the suggestion she would be overtly partisan as a senator by naming which Republican colleagues she might be able to work with in the Senate.

She immediately named Senator Richard Lugar of Indiana, even though he is leaving Congress in January after being beaten in his own party primary earlier this year. Brown and Gregory replied in unison, “He’s not going to be there.’’

Warren then backpedaled, saying, “But he’s not going to be there, and that’s a problem.’’

She then tried to right herself by avoiding specifics and saying, “It depends on what the subject matter is.’’

That fueled Brown’s argument that in an overtly partisan political landscape that has exasperated and turned off many voters, he is a more bipartisan figure than Warren, putting aside, that is, his choice of ultraconservative Antonin Scalia when asked to name his model Supreme Court Justice — a moment that again elicited boos from liberals in the audience.

Warren, he said repeatedly, would be less likely than he to cross the aisle and work with the rival party.

“With regard to working with any person on the opposite side of the aisle, she couldn’t reference one person except for someone who is retiring, a truly bipartisan gentleman, Senator Lugar. I have a history since Day One,’’ Brown said.


Most recent polls have shown Warren with a slight lead over Brown, not an especially good place for him given that Democrats are counting on big turnout on Election Day with President Obama on the top of the ticket.

As he did throughout the debate, Brown focused on Warren’s character as a means to disqualify her from taking his seat. Yet Warren did not lack ammunition to respond.

Both Gregory in his questioning, and Warren in her counterattacks, forced Brown to explain how — with the security of a full, six-year Senate term, and the Republican Senate and White House he seeks — he would retain his bipartisan character.

In two cases, his explanations strained credibility against the clear realities of party life in Washington.

First, asked if he would support Senator Mitch McConnell of Kentucky to be majority leader in the Senate, Brown replied, “I have already let it be very clearly known to Mitch McConnell that I’m completely disgusted by what’s going on down there. And he has a lot of work to do to earn my vote.’’

The truth, though, is that McConnell’s name will be the only one on his party’s ballot.

And when asked if he would support the economic plan rolled out by a hypothetical President Mitt Romney, Brown also tried to maintain an unlikely distance from his party’s leader. “I want to read them, see how they affect Massachusetts, our country, and our deficit, and vote,’’ he replied.

For Brown the Republican to win enough votes in what remains heavily Democratic Massachusetts, he has to convince a lot of voters he is sincere in those statements.