An overbearing and at times ridiculously aggressive Massachusetts Senator Scott Brown came across as a desperate man Thursday night, as he attempted to gain the upper hand in the first debate of this year’s most closely watched US Senate race and, by extension, in a re-election contest that seems to be slipping away from him.

Brown attacked Elizabeth Warren, his surging Democratic challenger, from start to finish.

Warren, unruffled and showing the confidence of a woman who has moved ahead of Brown in most recent polls, sometimes rolled her eyes or shook her head in disappointment. She made her points about Wall Street wrongdoing and holding corporations to account, about ending the war on women and making sure Mitt Romney and a Republican Senate do not fill the next vacancies on the US Supreme Court. Brown could attack all he wanted, but the senator who joined fellow Republicans in trying to block President Obama’s nomination of Elena Kagan to the High Court could not change the reality that Warren was right when she said, “This really may be the race for the control of the Senate and the Supreme Court may hang in the balance.”

Warren was smooth and effective, “explaining things” with the same assurance that Bill Clinton displayed in Charlotte. It wasn’t always easy; as Brown interrupted at every opportunity—to accuse Warren of lying about her heritage, of attacking asbestos victims, of starting Occupy Wall Street.

But Warren never sweated it. She knew she had the winning hand. And she played it. Again and again.

In a very Democratic state that very much does not want Republicans to take control of the US Senate, Warren kept emphasizing that—for all Brown’s talk of bipartisanship and reproductive rights moderation—“It’s not about Senator Brown’s vote. It’s about the votes of all the Republican senators.”

Noting again and again that Brown had told Republican donors across the country that they needed to help him win re-election so that Republicans can take charge of the chamber, Warren kept returning to a basic theme: “This is about control of the Senate.”

That was a powerful message, and a correct one.

But the even more powerful message came when Warren declared midway through the debate: “This really is about who you want as commander-in-chief.”

In a state that once elected Mitt Romney governor but that will never vote for him again, Warren drew the line of distinction that her opponent feared most—and that Republican candidates in other states are view with mounting trepidation as the Romney campaign stumbles from candidate-created crisis to candidate-created crisis.

“I support President Obama,” she said.

Brown just gulped.

He knows he’s got a problem. That problem is named Mitt Romney. And it got a whole lot worse when Romney attacked 47 percent of Americans as a “dependent” class that he can’t be bothered with.

On the eve of the first debate in the 2012 election season’s most intense contest, a Massachusetts group made a simple request of Scott Brown.

Progress Massachusetts asked the senator to level with the voters about where exactly he stands with regard to Mitt Romney and Paul Ryan. Does supposedly moderate Brown think the country would be better served with the most extreme Republican ticket in the party’s history assuming executive authority over the United States? And, if that is the case, how exactly will he help them to exercise that authority?

Basic questions. Easily answered.

Except by Scott Brown, whose debate performance Thursday night offered a striking example of how a career politician can talk out of both sides of his mouth without saying anything of consequence.

Brown kept trying to suggest that a handful of reasonably moderate votes made him a paragon of bipartisan virtue who should not be seen as a Republican.

In contrast, Warren, the Wall Street reformer and consumer champion who entered the Senate race with a real determination to change Washington—even if it means standing up to her own party—was clear and unequivocal.

“I want [President Obama] to stay on as commander in chief,” she declared.

The contrast between Brown and Warren could not have been more stark. But the real debate was and is between Brown and Brown.

The senator has objected to the Republican platform of Mitt Romney and Paul Ryan, decrying the document’s extreme and inflexible language on social issues as “a mistake.” The senator has distanced himself from his party’s vice presidential nominee, noting that he voted twice to block Senate consideration of Ryan’s signature proposal, the “Roadmap for America’s Future.” And the senator has loudly rejected Romney’s rejection of 47 percent of Americans, saying “That’s not the way I view the world.”

Yet, Brown still wants to have it both ways. He wants conservative backers of the Romney-Ryan ticket to think he’s with them. He wants moderate and liberal independents, and even some Democrats, to see him as a renegade Republican who has no taste for the ticket.

That’s political gimmickry, and Progress Massachusetts executive director Michael Fogelberg—a veteran Massachusetts activist with decades of experience as a tenant organizer and consumer and environmental campaigner—called him on it.

In a letter delivered to Brown, Fogelberg wrote:

The Republican nominee for President—your endorsed candidate—has said in no uncertain terms that he believes that nearly half of America believes that they are ‘victims’ who do not ‘care for their lives.’ Mr. Romney cannot credibly serve as the Commander in Chief of our nation when he so clearly has such contempt for half of our nation’s population.

“As such,” Fogelberg continued, “Senator Brown, I urge you to immediately, and in no uncertain terms, rescind your endorsement of Mitt Romney for President. Failure to do so is tantamount to an endorsement of Mr. Romney’s reprehensible and divisive remarks. Any half-measure, such as a mere Tweet criticizing the comments, would be seen as a cynical political ploy.”

But Brown’s entire career has been a cynical political ploy. He’s got to keep the conservative money flowing. So it is hard to imagine that he will renounce Romney, and he certainly is not going to oppose his Republican caucus when it comes to organizing the Senate

Elizabeth Warren would have won the debate on points. But she knocked Brown out with a one-two punch: “Republican Senate” and “Mitt Romney.”

Check out more of John Nichols’s coverage of Scott Brown’s Mitt Romney problem.