Sen. Patty Murray has won a fourth term, riding a wave of strong Democratic support in King County to defeat Republican challenger Dino Rossi.
Rossi conceded at about 6 p.m., calling Murray to congratulate her, according to a statement released by his campaign.
"I ran for the Senate because I believe we need a basic course correction from where Washington, D.C., has been taking us and to make sure this country is as free, as strong and as prosperous in the future as it has been in the past to preserve the best of America for future generations," Rossi said in the statement.
"That was a message that found a very receptive audience all across this state, though not quite receptive enough," he said.
Rossi said he hoped both political parties would work together in the next few years to solve the country's problems, especially the economy and massive federal debt.
As of Thursday evening, Murray was leading Rossi by more than 45,000 votes, taking 51 percent to Rossi's 49 percent. That's up from a 14,000-vote lead on Election Day.
According to a Seattle Times analysis, Rossi would need to get about 54 percent of the estimated 591,000 uncounted ballots statewide to overcome Murray's lead.
But nearly 264,000 of those ballots are in King County. Murray's already commanding lead there has only expanded since Election Day. She took 68 percent of the 69,000 King County ballots counted Thursday.
To overcome King County's heavy support for Murray, Rossi would have to take about two-thirds of the remaining ballots in the rest of the state. So far he's received 53.2 percent of those non-King County votes.
That made Rossi's task virtually impossible, even though hundreds of thousands of ballots remain to be counted statewide.
Murray planned to hold a news conference Thursday night.
Her victory helped Democrats maintain a majority in the U.S. Senate in a year that saw many Democratic incumbents fall, and the Republicans seize control of the U.S. House.
It was the third statewide defeat for Rossi, who is a former state legislator and a real-estate investor from Sammamish.
Rossi lost the bitterly contested 2004 gubernatorial race to then-Attorney General Chris Gregoire, after two recounts and a failed lawsuit. He lost to Gregoire by a wider margin in 2008.
Jim Brunner: 206-515-5628 or email@example.com