WASHINGTON • Republicans were closing in Wednesday on a narrow House majority while control of the Senate hinged on a series of tight races in a midterm election that defied expectations of sweeping conservative victories driven by frustration over inflation and President Joe Biden’s leadership.

Either party could secure a Senate majority with wins in both Nevada and Arizona — where the races were too early to call. But there was a strong possibility that, for the second time in two years, the Senate majority could come down to a runoff in Georgia next month, with Democratic Sen. Raphael Warnock and Herschel Walker failing to earn enough votes to win outright.

In the House, Democrats kept seats in districts from Virginia to Kansas to Rhode Island, while many in states like New York and California had not been called. But Republicans notched several important victories in their bid to get to the 218 seats needed to reclaim the House majority. In a particularly symbolic victory, the GOP toppled House Democratic campaign chief Sean Patrick Maloney of New York.

Control of Congress will be a key factor in determining the future of Biden’s agenda and serve as a referendum on his administration as the nation reels from record-high inflation and concerns over the direction of the country. A Republican House majority would likely trigger a spate of investigations into Biden and his family, while a GOP Senate takeover would hobble the president’s ability to make judicial appointments.

Democrats, though, saw candidates who prioritized protecting abortion rights, after this summer’s Supreme Court decision overturning the landmark Roe v. Wade court decision, perform well. The party won governors’ races in Wisconsin, Michigan and Pennsylvania — battlegrounds critical to Biden’s 2020 win over Donald Trump. But Republicans held on to governors’ mansions in Florida, Texas and Georgia, another battleground state Biden narrowly won two years ago.

Even if the GOP wins the House, it won’t be by a margin as large as during other midterm cycles. Democrats gained a net of 41 House seats under Trump in 2018, President Barack Obama saw the GOP gain 63 gain in 2010 and Republicans gained 54 seats in 1994, during the Bill Clinton administration.

A small majority in the House would pose a great challenge for the GOP and especially California Rep. Kevin McCarthy, who is in line to be House speaker and would have little room for error in navigating a chamber of members eager to leverage their votes to advance their own agenda.

In Pennsylvania, Democrats won the governorship and Senate in the key battleground state. Lt. Gov. John Fetterman, who suffered a stroke five months ago, flipped a Republican-controlled Senate seat, topping Trump-endorsed Republican Dr. Mehmet Oz. In the governor’s race Democratic Attorney General Josh Shapiro beat Republican Doug Mastriano.

In Wisconsin, Republican Sen. Ron Johnson prevailed over Democratic Lt. Gov. Mandela Barnes, while in New Hampshire, Democratic Sen. Maggie Hassan beat Don Bolduc, a retired Army general who had initially promoted Trump’s claims about the 2020 election.