Patty Murray's stint as the Senate Democrats' chief strategist this election culminated Wednesday with her party expanding control of the chamber by two seats, thanks to two Democratic wins not even Nate Silver, the political forecasting whiz, expected.

WASHINGTON — Patty Murray’s stint as the Senate Democrats’ chief strategist this election culminated Wednesday with her party expanding control of the chamber by two seats, thanks to two Democratic wins not even Nate Silver, the political forecasting whiz, expected.

The victories by incumbent Sen. John Tester in Montana and by Heidi Heitkamp in North Dakota mean Democrats will have a 54-45 edge in the Senate in January. They may get a further boost, 55-45, if incoming independent senator from Maine, Angus King, decides to caucus with the party.

Many pollsters had expected Republicans, not Democrats, to make pickups in the Senate. Murray shied away from publicly predicting gains, saying she hoped Democrats would retain their majority.

She said Wednesday that the election vindicated her strategy as chair of the Democratic Senatorial Campaign Committee to recruit candidates who reflected the American electorate.

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“I really went out to find people who understood what was happening to families in this country,” Murray said.

She said that gave her faith in her candidates, some of whom were considered longshots. Heitkamp, for instance, edged out Republican Rep. Rick Berg by fewer than 3,000 votes. Silver, who correctly called 50 states in the presidential race, had North Dakota as a virtual lock for the Republicans.

Montana’s Tester — rated by Silver and other pollsters as a soon-to-be former incumbent — won a comfortable victory.

Murray and the Democrats were defending 23 Senate seats while the GOP had only 10 seats up for re-election.

In all, Democrats flipped three Republican-held seats in Massachusetts, Indiana and Maine while losing only Nebraska. King, a former Maine governor, ran as an independent and has not said which party he plans to caucus with. But Democrats are counting on King, who endorsed President Obama, to cast his lot with them.

Murray also focused on fielding female candidates this year. That paid off with four new Democratic female senators, including Elizabeth Warren of Massachusetts and Tammy Baldwin of Wisconsin. They, along with Republican Deb Fischer of Nebraska, will join a class of 20 female senators in January, breaking the record of 18 in the last Congress.

Murray believes the infusion of estrogen — Democratic and Republican — will bring a much-needed propensity for bipartisanship. “I think that dynamic will really help move us to solve some of the problems that have been plaguing us for a long time,” she said.

Kyung Song: 202-383-6108 or ksong@seattletimes.com