One race in Georgia is headed to a January runoff. A second contest in Georgia and races in North Carolina and Alaska remain undecided, leaving the chamber now deadlocked 48-48. An outcome may not be known until the new year.
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With the presidential race between President Donald Trump and Democrat Joe Biden also undecided, the Senate is in limbo because the vice president of the eventual winner's party would serve as a tie-breaker in a split chamber.
"We're waiting - whether I'm going to be the majority leader or not," Senate Majority Leader Mitch McConnell, R-Ky., said Wednesday.
That was still the case Thursday.
The counting continued in Georgia, where GOP Sen. David Perdue was trying to hold off Democrat Jon Ossoff in a multi-candidate race that could also go to a runoff if neither candidate clears the 50% threshold to win.
There already is a Jan. 5 runoff in the state's other Senate race. GOP Sen. Kelly Loeffler will face Democrat Raphael Warnock, a Black pastor at the church where the Rev. Martin Luther King Jr. preached, after they emerged as top vote-getters, but failed to clear the majority threshold.
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In North Carolina, GOP Sen. Thom Tillis hoped to prevail over Democrat Cal Cunningham, whose sexting affair with a public relations specialist has clouded the race.
Republicans were confident they would keep Alaska, where GOP Sen. Dan Sullivan was challenged by newcomer Al Gross, a doctor and Democratic-backed independent.
Democrats faced long but not fully impossible odds to take a slim majority after a disappointing election night when Republicans defeated multiple challengers.
In Michigan, Democrats were spared a loss when Sen. Gary Peters withstood a strong challenge from Republican John James, a Black Republican businessman. But Republicans held on to Susan Collins in Maine and other key seats.
McConnell, who secured a seventh term for himself in a costly campaign against Democrat Amy McGrath, a former fighter pilot, has said he he felt "pretty good" about the remaining contests.
But Democrats remained hopeful. Strategist Zac Petkanas said the 2020 election "was going to be an awful, ugly, dirty slog until the bitter end."
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Election night jarred Democrats and enthusiastic backers who were eager to counter Trump and his party's grip on the Senate.
While Democrats picked up must-win seats in Colorado and Arizona, they suffered a setback in Alabama, and Republicans held their own in one race after another - in South Carolina, Iowa, Texas, Kansas and Montana. That dramatically limited Democrats' hopes to make inroads.
In Maine, Sen. Susan Collins' victory over Democrat Sara Gideon was especially important for Republicans, holding a seat in a state where Trump was not expected to win. For Collins, it was the hardest-fought race of her career. Democrats had tried to tie the moderate to Trump and criticized her for her vote to confirm Justice Brett Kavanaugh in 2018.
Many races attracted an unprecedented outpouring of small-dollar donations for Democrats.
"You wasted a lot of money," said White House ally Sen. Lindsey Graham, R-S.C., after defeating Jaime Harrison, despite the Democrat's stunning $100 million haul for his upstart campaign.
But Harrison energized voters, among several Black Democratic candidates for Senate including Warnock, drawing an outpouring of national support in a year of racial reckoning, enthusiasm that will be tested again in 2021.
"This is the most important race in the country right now," Warnock said in a fundraising appeal.
Securing the Senate majority will be vital for the winner of the presidency. Senators confirm administration nominees, including the Cabinet, and can propel or stall the White House agenda. With Republicans now controlling the chamber, 53-47, three or four seats will determine party control, depending on who wins the presidency.
The Democrats' gains were in Colorado where former Gov. John Hickenlooper defeated GOP Sen. Cory Gardner, and Arizona, where former astronaut Mark Kelly beat Republican incumbent Martha McSally.
But Democrats couldn't hold on in Alabama: Former college football coach Tommy Tuberville defeated Sen. Doug Jones.
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House Democrats blame losses on polls, message, even Trump
Their majority shrunk, House Democrats cast blame Thursday on their election message, ground game and leadership under Speaker Nancy Pelosi's team after expectations for big wins came crashing down by a stark reversal in Trump country.
They focused too narrowly on health care, when voters were also worried about the economy.
They failed to fight back when Republicans labeled them "socialists" aligned with the party's most liberal firebrands.
They didn't knock on doors to meet voters, focusing instead on phone calls, digital outreach and TV ads, due to the health risks of campaigning during the pandemic.
They lost Latino voters in some places, and white, working class men in others.
They did not pass more COVID aid through Congress when Americans needed help most.
And perhaps most importantly, Democrats are coming to grips with the fact that whether President Donald Trump is e-elected or defeated by rival Joe Biden, they still have a problem understanding and winning over Trump voters.
Lawmakers unloaded during a caucus call Thursday - Democratic freshman Rep. Abigail Spanberger, in a so-tight race in Virginia, spoke with "passion" about the party's campaign failures, according to a person familiar with the private call and granted anonymity to discuss it.
The marathon call ran three hours, with some 30 members adding their views.
No one spoke against Pelosi, who tried to remind them, they did, in fact, win: Biden is on the verge of replacing Trump, and House Democrats are on track to keep their majority, according to another person familiar with the call and granted anonymity to discuss it.
"We did not win every battle but we did win the war," Pelosi said.
But there were plenty of complaints to go around - over faulty polling, Republican attack ads - as expectations had been raised sky high for election night gains and that made the setbacks all the more disorienting.
Rather than bolstering their majority, as planned, Democrats lost a handful of freshman lawmakers who had just won in a 2018 midterm election backlash against the president. They also failed to add to their ranks as Republicans defeated one Democratic challenger after another.
Asked what went wrong, one Democratic strategist granted anonymity to frankly run through the list shortcomings, said: "All of the above."
Money, with the onslaught of campaign cash flowing to Democrats in an anti-Trump revolt, was the one thing on their side. But money alone was not enough.
Key Democrats said the GOP attacks against them as wild-eyed "socialists" are damaging, as are some of the party's most liberal proposals.
They cited the "defund the police" movement that calls for shifting law enforcement resources to social workers and other ways of revolving conflicts. It gained prominence last summer after the police killing of Black people, including George Floyd, sparked a nationwide reckoning on racial injustice. Democrats also were criticized this year as insufficiently supporting Israel because of a liberal proposals helping Palestinians.
"I think that the Democratic party needs to clearly push that we are not supportive of ideas like socialism or defunding the police or anti-Semitism," said Rep. Stephanie Murphy, D-Fla., a co-chair of the House's centrist Blue Dog Coalition.
Several Democrats said the "socialist" label particularly harmed lawmakers who lost seats in Florida with its vast Cuban and Venezuelan communities who largely reject socialist ideologies.
Murphy said the House leadership team was putting "lipstick on a pig" by touting the overall election outcome as a success.
"This playing footsies with socialism is not going to win over most of America," she said. "There's no amount of lipstick that can cover up the fact that these far left ideas are costing us races."
But progressive ideas were also defended on the call, said another person granted anonymity to discuss it.
Other Democrats argued it was always going to be difficult to defend the House majority. It was won in 2018 with more women and minority candidates in history, reaching into districts Trump had won in 2016. Holding onto those seats would be tougher once the president was back on the ballot.
In defeating Democrats, Republicans filled many of the seats with more women and minority candidates than ever, after their ranks of both had dwindled to single digit numbers in the House.
Democratic freshman Rep. Elissa Slotkin, who won re-election in Michigan, did so with a more narrow margin than she did in 2018.
"With President Trump on the ballot, it just drove enormous turnout that was almost impossible to surmount" in some areas, she said.
Other lawmakers in Oklahoma, New Mexico and South Carolina did not fare as well, and were defeated.
Rep. Tom Emmer, R-Minn., the brash former hockey player, delighted after the GOP wins in reminding people that Democrats laughed when he first rolled out the Republican plan for the election.
"Our message from day one was that the Democrats' radical socialist agenda is a threat to middle-class Americans," he said on Wednesday conference call with reporters.
The Democrats, he said, "should have listened."
Polling was clearly a problem, on all sides, strategists said. Republicans, too, thought they were heading toward losses but instead made gains.
But they also need to learn how to win back the Trump voters they have lost.
"Is there something that we're missing about these Trump voters? said Rep. Ami Bera, D-Ca., a member of the centrist House New Democrat Coalition. "Because we certainly saw a lot of Trump voters show up."