AND THEN THERE WERE 53…. There were two unresolved U.S. Senate races going into yesterday, but last night, the close contest in the state of Washington was called in the Democrats’ favor.

Senator Patty Murray of Washington State has won a fourth term, narrowly defeating her Republican challenger Dino Rossi, who conceded Thursday afternoon.

Her victory brings the number of Democratic seats in the Senate to 53, and reinforces a trend in which Democrats on the East and West Coasts were able to fight off Republican challengers while those in the South and Midwest were defeated. […]

He conceded after Ms. Murray’s lead widened with the latest vote counts from King County, home of Seattle and a trove of Democratic votes. Both The Associated Press and The Seattle Times called the race Thursday afternoon for Ms. Murray.

The outcome of the race in Alaska is still unclear, though Sen. Lisa Murkowski appears to have won, but the result won’t affect the partisan makeup of the next Senate — the remaining candidates are both Republicans.

As such, we now know that the next Senate will have a 53 to 47 Democratic majority (though two members of the Democratic caucus are independents). Democrats have now won a Senate majority for three consecutive cycles, the first time that’s happened since 1992. Oddly enough, Mitch McConnell neglected to mention this yesterday when demanding that everyone respect his authority.

Also note, while Republicans defeated a whopping 49 House Democratic incumbents this week, the grand total of Senate Democratic incumbents who were defeated this week was two: Blanche Lincoln and Russ Feingold.

It’s speculative, of course, but I suspect if you’d told Democratic leaders a few months ago that they would have a 53-47 majority next year, they’d not only have been surprised, they’d probably have been rather giddy.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.