The U.S. Capitol on December 18, 2019 in Washington, D.C. (Photo by Samuel Corum/Getty Images)

WASHINGTON — Democrats gained at least one Republican-held seat in the U.S. Senate, but also lost a seat of their own and were unable to defeat several GOP incumbents in the elections, ending up early Wednesday with an increasingly challenging path to wresting control of the chamber away from Republicans.

The initial results showed a disappointing night for Democrats, and made the prospect of another two years of a politically divided Congress more likely, even as lawmakers struggle to come to an agreement on an economic relief package amid the pandemic.

In Colorado, Democrats succeeded in flipping the seat held by GOP Sen. Cory Gardner, a first-term lawmaker seen as one of the most vulnerable Senate Republicans this cycle. He struggled in his reelection race against Democratic former Gov. John Hickenlooper, who also sought the presidential nomination this year.

“Regardless of which party ends up controlling the Senate, I want you to know what I will work with anyone and everyone to help Coloradans,” Hickenlooper said.

Gardner pledged to assist Hickenlooper in the transition, and called for unity: “Please understand, to all the people who supported our efforts tonight, that his success is Colorado’s success, and our nation and our state need him to succeed.”

At the same time, Democrats, as predicted, lost a seat in Alabama. Sen. Doug Jones was defeated by Republican candidate Tommy Tuberville, former head football coach at Auburn University. The Associated Press called the Alabama race.  

Other Senate Republicans that Democrats had targeted held off their challengers.

In a neck-and-neck contest in North Carolina, Democrat Cal Cunningham had an early lead, but GOP Sen. Thom Tillis closed the gap as results trickled in for a 96,000-vote lead with 94% reporting. The AP and other news outlets hadn’t called the race when Tillis declared victory shortly before midnight.

“I have a very hard time right now seeing how Democrats win back the Senate,” Jessica Taylor, a Senate analyst with the nonpartisan Cook Political Report, tweeted early Wednesday morning, adding that the remaining path was “not impossible, but looking unlikely.”

Democrats headed into Election Day well-positioned to potentially regain a majority in the Senate, where Republicans hold 53 seats to the Democrats’ 47 (a tally that includes two independents who caucus with the party). 

Flipping partisan control would require Democrats to pick up four seats, or just three if Democratic presidential nominee Joe Biden claims the White House, since his vice president would break any ties on the Senate floor. 

Which party controls the Senate will have significant implications for the next president and his agenda. On the other end of the U.S. Capitol, Democrats were projected on Tuesday to maintain a majority in the U.S. House. If Biden secures enough votes to become president, his policy agenda could be blocked by a GOP Senate — and a Democratic one could give him the votes to sign his top priorities into law.

The clearest path for Democrats to flip the Senate was through winning GOP-held seats in Arizona, Colorado, Maine, and either Iowa or North Carolina, according to analysts who track those races. But final results for most of those races had yet to come late Tuesday, as polls closed across the country.

In Arizona, Democrat Mark Kelly had a 10-point lead over Republican incumbent Martha McSally with 76% of votes reported. But in Iowa, Republican incumbent Joni Ernst held off Democratic challenger Theresa Greenfield after a close and historically expensive race there. And in Maine, Republican incumbent Susan Collins led Democrat Sara Gideon, 52% to 41%, with two-thirds of votes tallied. 

Another Republican incumbent defended his seat from a Democratic challenger. In Montana’s Senate race, Sen. Steve Daines beat the state’s current governor, Steve Bullock, with 53% percent of the votes as reported by the AP. 

Meanwhile in Michigan, early results showed Democratic Sen. Gary Peters trailing his Republican challenger, businessman and Iraq War veteran John James, but significant numbers of mail ballots remained to be counted there.  

Georgia has two Senate races, where several scenarios can play out and the outcome of each race could take up to days or even weeks. In each race, a candidate needs to get more than 50% of the votes or else a runoff election will be held on Jan. 5 with the top two candidates. 

One race is a special election with Sen. Kelly Loeffler, who was appointed last year after Sen. Johnny Isakson stepped down due to health problems. As of late Tuesday, Democratic Senate candidate Raphael Warnock had a slim lead over Loeffler, but neither candidate passed the 50% percent threshold needed to avoid a runoff. Another Republican candidate in Georgia’s special election, Doug Collins, wrote on Twitter that he called to congratulate Loeffler, as she would be the Republican candidate in a runoff election.

“I look forward to all Republicans coming together,” he wrote. “Raphael Warnock would be a disaster for Georgia and America.”

Georgia’s other race, between incumbent Republican Sen. David Perdue and Democratic candidate Jon Ossoff, has not been called yet. However, Perdue late Tuesday had a lead above the 50% percent threshold.

Republican Sen. Lindsey Graham of South Carolina kept his Senate seat, according to The Associated Press, in a competitive race against his Democratic opponent Jaime Harrison, who brought in a whopping $107 million in fundraising. Democrats had hoped to upseat Graham, a close ally to the president who shepherded the nomination of Supreme Court Justice Amy Coney Barrett through the Senate.

Another Republican that kept his seat was Sen. John Cornyn of Texas, a member of GOP leadership. He beat his Democratic challenger, MJ Hegar, according to the AP. 

In Kansas, where the Senate seat held by Republican Pat Roberts was open, the AP declared Republican Roger Marshall the winner in the contest against Democrat Barbara Bollier.

But Democrats are defending far fewer competitive seats than the GOP is, an advantage that was bolstered by a polarizing Republican president whose struggles in the polls have not helped down-ballot Republicans. The party also kept its seat in Virginia, with Sen. Mark Warner’s reelection, which the AP called shortly after polls closed. Republican challenger Daniel Gade, who refused to concede Tuesday night and slammed the AP, acknowledged defeat late Wednesday morning.

Democratic Sen. Tina Smith of Minnesota also kept her seat from her challenger, Republican candidate Jason Lewis, which the AP called. She won nearly 50% of reported votes.

Democrats also were boosted by a flood of campaign cash, as Senate races across the country shattered political fundraising records. 

As of mid-October, eight of the top 10 most expensive Senate races have taken place in the 2020 cycle, according to the Center for Responsive Politics. And in Senate races, Democrats outraised Republicans, pulling in $726 million to Republicans’ $423 million through September

In Kentucky’s Senate race, Democratic nominee Amy McGrath raised $88 million in funding, but Senate Majority Leader Mitch McConnell won his reelection campaign. He raised $55.5 million.

 UPDATE: This story has been updated to reflect new election results and the concession of Virginia Sen. Mark Warner’s opponent.