Sen. Patty Murray has been re-elected to a fourth term.

The incumbent picked up a net gain over Republican Dino Rossi of more than 25,000 votes from King County Thursday afternoon, almost doubling her statewide lead .

Rossi conceded shortly after the results were posted.

“This evening, I called Senator Murray to offer my congratulations on her re-election to the U.S. Senate,” he said in a statement. “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.”

The Associated Press and The Seattle Times both called the race for Muray. Her win cushions the Democrats’ advantage in the Senate, giving them 51 members and two independents who caucus with them. The GOP retook the House this week.

The incumbent now leads Rossi by about 46,000 votes out of 1.8 million cast. After Wednesday’s tally, Murray led Rossi by 27,436 votes out of about 1.62 million counted statewide. After Tuesday’s first count, that lead had been just 14,005 votes out of 1,430,787.

Murray was besting Rossi 309,877 votes to 178,725 in King County. Every day, the margins for Murray in the state’s largest county have improved. She’s now taking more than 63 percent of the vote in King; on Election Night that number was just over 62 percent.

In King County, Murray’s advantage over Rossi is now 131,152 votes. As of Wednesday, it was 105,639 – a pickup of 25,513 votes.

Election officials had figured that about 2.4 million total votes would be cast in Washington, but that was an estimate. Best on pre-election estimates, there are likely more than 200,000 ballots left to be counted in King County.