WASHINGTON — The new Congress will be slightly more Democratic and more female, though House Republicans still hold a majority large enough to confront and confound President Obama as the nation grapples with a slow-moving economic recovery and record deficits.
Senate Democrats, once scrambling to save vulnerable incumbents and their tenuous numerical advantage, surprisingly gained a net of two seats as undecided races were settled Wednesday. The final results gave women a high-water mark of 20 in the 100-member chamber as Hawaii’s Mazie Hirono, Nebraska’s Deb Fischer, Elizabeth Warren of Massachusetts, Tammy Baldwin of Wisconsin, and Heidi Heitkamp of North Dakota were elected to join 15 returning female senators. Of the new female senators, all but Fischer are Democrats.
‘‘I think what women bring to our Senate is a reality that voters across the country understand and reflect,’’ said Senator Patty Murray, a Democrat of Washington who was chairwoman of her party’s campaign committee. ‘‘When they see women speaking, there are people who say, ‘I understand that.’ ”
In Montana, Senator Jon Tester, a Democrat, turned back a challenge from Representative Denny Rehberg, a Republican, when the vote count wrapped up Wednesday. In North Dakota’s open race, the GOP candidate, Representative Rick Berg, conceded to Heitkamp, the former state attorney general.
Democrats will hold 53 seats to 45 for the Republicans, with the certainty that Bernie Sanders, a Vermont independent, will align with the Democrats and the expectation that Maine’s Angus King, an independent, will do the same to give Democrats an effective 55-45 majority. King said he could make a decision as early as next week when he heads to Washington. He received a congratulatory call from Senate majority leader Harry Reid of Nevada but said he never heard from the Republican leadership.
In the House, Republicans will have a smaller majority, but not so small that it affects their ability to control the chamber’s agenda and challenge Obama and Senate Democrats.
‘‘The message I got is Americans don’t want a runaway Congress and administration,’’ said Representative Greg Walden of Oregon, who is expected to head the Republicans’ campaign committee next year. ‘‘If they wanted one-party control, they could have done that this election cycle.’’
With only a smattering of House races still undecided, Republicans had won 233 seats; were assured of another after a December runoff between two Louisiana Republicans; and led in an Arizona contest. That is well more than the 218 needed to control the chamber, but less than the 242 seats they now hold.
Ten members of the Tea Party-backed freshman class of 2010 lost; 83 of them had sought reelection. Representative Allen West of Florida, a freshman Tea Party champion, was behind the Democratic challenger, Patrick Murphy, by nearly 2,500 votes but refused to concede. It was the most expensive House race in the country, with the two rivals and their allies spending a combined $23.8 million, about two-thirds of it for West. Among other losers were Nan Hayworth of New York and Frank Guinta of New Hampshire.
Several high-profile conservatives won their tough races, including Steve King in Iowa and Michele Bachmann, a former presidential candidate, in Minnesota.
Around 30 or 40 House Republicans — not all of whom were freshmen in 2010 — have proven difficult for GOP leaders to corral on some issues, including on compromises eventually reached with Obama and Democrats over averting government shutdowns and defaults.
Democrats won 192 seats and led in eight races, giving them up to 200 seats next Congress. They controlled 193 this year, including three vacancies.
It remained unclear Wednesday whether former House speaker Nancy Pelosi will seek to lead the party in the next Congress. In September, the Democrat of California told reporters that it would be up to her fellow Democrats and her family ‘‘after all this time’’ to decide her fate.