Democratic Sen. Maria Cantwell's extremely narrow victory against a GOP incumbent in 2000 has landed her current race against challenger Mike McGavick on the midterm must-watch list. The race is widely viewed as the Republicans' best chance to unseat a Democratic senator this fall.

In 2000, Cantwell defeated prominent Republican incumbent Slade Gorton by only 2,229 votes in the year's closest Senate race. This year, summertime polls gave Cantwell a comfortable early lead, but gains by McGavick and the possibility that he may dedicate substantial personal wealth to the campaign leave the seat up for grabs.

Although known for a reserved personal style, Cantwell has proven herself a determined and aggressive campaigner. She outspent Gorton by over $5 million to claim his seat in 2000, self-financing her campaign to the tune of $10.3 million. As a strong supporter of McCain-Feingold-style campaign finance reform, Cantwell has often heard criticism of her largely self-financed run in 2000.

This year, the shoe is on the other foot.

With a reported worth of between $36 million and $65 million, McGavick stands able to give his campaign a significant financial boost. In mid-August, he contributed $2 million dollars to his campaign. Anticipating this move, Cantwell in July asked the Federal Election Commission to clarify the state's Millionaires' Amendment. The provision allows a candidate to increase individual campaign contribution limits to match the personal financing of wealthy opponents, and Cantwell hoped to trigger the amendment before the Sept. 19 primaries.

On Aug. 29, the FEC ruled in McGavick's favor saying that, in advance of the primaries, the Millionaires' Amendment only applies to challengers within his own party.

Cantwell reportedly will not self-finance this year. She has seen her personal wealth fall from a reported $40 million during her 2000 campaign to an estimated current level of between $2.1 million and $10.3 million. Her largest financial asset is her stock in RealNetworks, the Washington-based software company she led before her election, which is valued between $1 million and $5 million.

Cantwell's political experience traces back to her childhood in Indiana, where she was born on Oct. 13, 1958. She has often attributed her interest in politics to her father, a construction worker, member of the union faithful, and outspoken Democrat who was active in local politics and also served as a state legislator.

Cantwell graduated from Miami University of Ohio in 1981 and worked for Jerry Springer's 1982 unsuccessful bid for the Ohio governorship. She then joined Sen. Alan Cranston's presidential campaign and moved to Seattle in 1983 to establish Cranston's regional office.

Cantwell was herself elected to the Washington House of Representatives in 1986, at the age of 28. In 1992, she won the race for U.S. House to represent Washington's 1st District. But Cantwell was ousted in 1994 when Republicans took over the House and Senate, losing to challenger Rick White by a narrow margin. By the time of her decision to run for Gorton's seat in the 2000 election, Cantwell had become an executive of RealNetworks.

In the race to retain her seat, Cantwell's platform emphasizes issues ranging from fiscal responsibility and immigration policy to health care, education and Social Security. Some of her strongest stances have been on the environment.

In December 2005, Cantwell helped quash an attempt by Sen. Ted Stevens, R-Alaska, to open the Arctic National Wildlife Refuge in his home state to oil drilling. Seattle Post-Intelligencer columnist Joel Connelly emphasized the importance of this move in a state where environmental issues rank among voters' chief concerns. "For a freshman senator to get 43 votes to sustain a filibuster on a defense bill in December, it bespeaks of both ability and guts," he said.

Cantwell also has weighed in on energy issues. She took oil companies to task for earning record profits during periods of high gas prices, and has proposed legislation to outlaw market manipulation.

Cantwell's 2002 support for the Iraq war resolution, however, has put her at odds with her Democratic base. She has since criticized the Bush administration's handling of the conflict, and in June supported an amendment that called for the withdrawal of U.S. troops without setting a definite timetable.

The senator did not voice a strong change of stance on Iraq until an Aug. 14 statement that read: "If I knew then everything that I know today and the Republican leadership still brought it up for a vote, I would have voted no."

Weighing Cantwell's chances this fall, Seattle Times chief political reporter David Postman observed that Washington has no Ned Lamont -- the vocal anti-Iraq war candidate who beat Sen. Joseph Lieberman in Connecticut's Democratic primary. Without such an anti-war challenger, Postman said he didn't expect Cantwell's Iraq position to harm her bid. "There are other things on the ballot that will drive turnout," he said. "I don't think that Cantwell's problems with the left will send that many people away."

-- Compiled by Molly Messick for the Online NewsHour