Washington -- This was to be the crowning year of California Sen. Barbara Boxer's career: More than three decades as a liberal environmental crusader had landed her at the helm of the Senate Environment and Public Works Committee, with lead jurisdiction over climate-change legislation. It was a chance to make history. But Boxer's legislation to limit carbon emissions died almost the moment it passed her committee on a party-line vote, amid a wall of GOP opposition. The breakdown crystallizes Boxer's vulnerability to the criticism from Carly Fiorina, her Republican challenger in November's general election, that she is a 'bitter partisan' who has 'little to show for her three terms in Washington.' While that criticism is overblown, it grazes a truth: Boxer tried to move a climate bill that was perceived as being too polarizing for such a heavy legislative lift. She handed the baton to Sen. John Kerry, D-Mass., to broaden support, while she staked out the liberal flank. No climate bill ever passed. Boxer, 69 , has built a political persona as a crusader, a self-described fighter for liberal causes, beginning with her first election to the Marin County Board of Supervisors in 1976. She has taken lonely and unpopular stands, from voting against the invasion of Iraq to forcing former Sen. Bob Packwood, R-Ore., to resign amid charges of sexual harassment. She was one of only 14 senators who voted against the Defense of Marriage Act , which was signed into law by President Bill Clinton in 1996 . 'You have to, at the end of the day, consider all the facts in front of you and vote your conscience on some of these questions, even if you're one of just a handful of people,' Boxer said in an interview. 'You remember those moments.' But when it comes time to build coalitions, she is not the senator people turn to. That role is played by Sen. Dianne Feinstein, Boxer's fellow California Democrat who was elected with Boxer in 1992 and has often overshadowed her. Feinstein has positioned herself as a pre-eminent dealmaker, often enraging liberals in the process. Boxer, who has built a reputation as a liberal stalwart, is not considered a swing vote. 'Boxer came in as the personification of Marin County,' said UC San Diego political scientist Samuel Popkin . 'Feinstein came in with the heroic profile. You can't have two Feinsteins at a time in one state. It just doesn't work, and Feinstein had this aura from San Francisco and beyond of being sort of the wise woman.' Boxer, he said, 'is more the pugilist fighter.' As a county supervisor from 1976 to 1982 , she sought to ban all nuclear power plants in California. As Marin's representative in Congress in 1991 , she led female colleagues up the Senate steps to protest the treatment of Anita Hill's allegations that Supreme Court nominee and now Justice Clarence Thomas had sexually harassed her. The protest was classic Boxer. It helped propel her to the Senate in the next year, the 'Year of the Woman.' Boxer has nurtured her crusader image. She wrote a book about the Anita Hill protest called 'Strangers in the Senate.' Her later autobiographical novel, 'A Time to Run,' is a narrative of liberal good battling conservative evil. 'I'm a fighter for the people I represent,' Boxer said. 'I have a very strong sense of when they're being hurt, and I'm not afraid to go up against the people that are trying to hurt my people. That's why I've got a lot of special interests that want me gone. Polluters want me gone. The far right, they want me gone.' Where Feinstein gave former Stanford University provost Condoleezza Rice a glowing introduction at her confirmation hearing to be Secretary of State in January 2005 , Boxer in the same hearing all but accused Rice of lying about weapons of mass destruction. By the same token, Boxer is a reliable and effective defender of liberal positions that come under attack. She negotiated a key compromise to protect abortion rights in this year's health care law. Although the climate bill failed, Boxer defeated an effort by Sen. Lisa Murkowski , R-Alaska, to nullify the Environmental Protection Agency's finding that greenhouse gas emissions endanger human health. While Boxer has said she votes with Feinstein nearly all the time, the two have diverged at critical moments. Boxer said her proudest Senate vote was a 'no' to the resolution on invading Iraq. Feinstein voted to allow the invasion. Feinstein voted for the 2001 Bush tax cuts; Boxer did not vote. Feinstein co-chairs Boxer's campaign committee and has said that while their styles differ, 'there is no daylight between us on the issues that matter most to Californians.' Boxer has teamed with Republicans far more than her reputation implies, on issues from designating a million acres of wilderness in California to a tax holiday for corporations with operations overseas to repatriate their earnings to the United States. Her environment committee has seen more of its bills enacted than under the three previous chairmen. One of her biggest bipartisan achievements was a giant water projects bill, the first legislation in which Congress overrode a veto by President George W. Bush. Bush said the bill spent too much and failed to set priorities. But in Congress, the water bill was intensely popular because it showered new projects on nearly every state. Boxer touts her work with Sen. Kit Bond, R-Mo., to buy more C-17 military cargo planes, rebuffing Defense Secretary Robert Gates' effort to terminate the program. The C-17 plant employs 1,700 workers in Long Beach . Boxer's support contrasts with her days as a House member who railed against President Ronald Reagan's defense buildup and criticized the Pentagon's purchase of a $600 toilet seat cover and a $7,622 coffee pot. Today, she says her most important accomplishment is the new combat care center in San Diego -- the West Coast equivalent of the Walter Reed Army Medical Center. After 18 years in the Senate, Boxer is no longer the obscure Marin crusader. She has amassed power, chairing the committee that has jurisdiction over not only climate change but also public works. She also chairs the Senate Ethics Committee and is just one rung below the top Senate leadership as Democrats' chief deputy whip. But facing the stiff headwind of a bad economy and an electorate, even in liberal California, that disapproves of deficit spending, Boxer's liberalism is less of an asset this year, said Mark DiCamillo, director of the Field Poll. 'Throughout all her tenure as senator, Boxer has more favorable to unfavorable ratings among California voters -- except for this year,' DiCamillo said. 'Voters are viewing her a lot more negatively now than they ever have. ... There's a generalized sense of overspending and a feeling that the budget should be managed more prudently and less expansively.' In Boxer's favor are the 2.3 million more Democrats registered in California than Republicans. And she has not lost an election since her first attempt to become a Marin supervisor in 1972 . Boxer defended her effort on the climate-change bill. 'I'm the only senator who ever got any climate-change bill through a committee, not only once but twice,' Boxer said. 'Nobody else has been able to do it, and the reason that I asked John Kerry, Lindsey Graham and Joe Lieberman to work for the 60 votes (needed to avoid a filibuster) is, I knew a broader coalition would be the only way we could get it done, because when you're a senator, you're not a CEO. You're part of a team.' Her job, Boxer said, was to hold together environmentalists who might rebel at the compromises necessary to get more votes. 'She's been a true stalwart and a true champion and highly effective,' said Sierra Club Chairman Carl Pope. 'I concede she couldn't pass a climate bill with 60 votes in this year's Senate, but it turned out nobody could.' 