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 called Murray at about 6 p.m. to concede, according to Alex Glass, Murray's deputy campaign manager.
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.
The Rossi campaign had no immediate comment.
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 makes Rossi's task virtually impossible, even though hundreds of thousands of ballots remain to be counted statewide.
Murray was with her family and unavailable for comment, a spokeswoman said. She was expected to hold a news conference later Thursday.
"Senator Murray had a strong showing on Tuesday night. She had a stronger showing yesterday and a stronger showing today. We feel very confident that she will be the winner of this race," said Murray spokeswoman Julie Edwards.
Murray's victory helps 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.