Democrats are defending the narrowest of Senate majorities in 2022 as Republicans look to fight their way back into power after a series of crushing defeats.
While Democrats are going on offense in a handful of states where GOP incumbents are retiring, the party is also facing strong national headwinds in their bid to hold onto the Senate. The party of a new president - in this case President Biden - almost always loses ground in Congress in midterm elections.
Given Democrats' slim Senate majority, control of the upper chamber is likely to come down to just a handful of states. Here are the 10 races that will decide the Senate majority next year:
With President Biden's narrow victory in the state last year and the coming retirement of Sen. Pat Toomey (R-Pa.), Pennsylvania may well offer Democrats their best chance to pick up a new Senate seat in 2022.
So far, more than half a dozen Democrats have entered the race to succeed Toomey, including Lt. Gov. John Fetterman, Rep. Conor Lamb (Pa.) and Montgomery County Board of Commissioners Chair Val Arkoosh.
And while the Democratic primary field has yet to yield a clear front-runner, the Republican field is just as fluid.
Sean Parnell, who had won former President Donald Trump's endorsement and was seen as the likely GOP front-runner, dropped out of the race last month amid a series of personal controversies, leaving a vacuum on the Republican side. The entrance of celebrity physician Mehmet Oz into the GOP primary in late November only served to shake up the race further.
Sen. Raphael Warnock (D-Ga.) is heading into 2022 fresh off a history-making victory in a January runoff, making the 2022 Senate contest in Georgia a test of whether Democrats can maintain their momentum in a state that has only recently become a battleground.
Republicans argue, however, that the state still leans in their direction, especially in a midterm year that is expected to be unfriendly for Democrats.
Former football star Herschel Walker, who has high name recognition in the state as well as Trump's endorsement, has emerged as the favorite for the GOP nomination. And while he still faces some primary opposition, top Republicans - including Senate Minority Leader Mitch McConnell (Ky.) - have coalesced around Walker, seeing him as the best candidate to oust Warnock next year.
Given both Trump's involvement in the race and Democrat Stacey Abrams's entrance into the contest for Georgia governor, the 2022 Senate election in Georgia is quickly emerging as the epicenter of the battle for control of the upper chamber.
Like Warnock, Sen. Mark Kelly (D-Ariz.) is heading into his 2022 reelection bid having just run a competitive race in 2020, and he's among the GOP's top targets in the Senate.
But before they can take on Kelly directly, Republicans will first have to resolve a relatively crowded primary.
While polling shows state Attorney General Mark Brnovich leading his rivals for the GOP nomination, Trump has somewhat complicated that picture by publicly taunting Brnovich for not doing more to reverse Biden's win in Arizona in the 2020 presidential election. Trump also appeared at a fundraiser for another GOP candidate, Blake Masters, at Mar-a-Lago last month.
The eventual winner of the Republican primary will have to contend with Kelly, one of the most prolific fundraisers in the Senate, in the 2022 general election. Still, with Democrats facing tough national headwinds next year, Kelly's seat is far from safe.
Sen. Ron Johnson (R-Wis.), one of the most despised figures by the left, hasn't yet said whether he will seek another term in the Senate in 2022, leaving Wisconsin Republicans in limbo for the time being.
The field of Democrats vying to take Johnson on, however, is vast. So far, Wisconsin Lt. Gov. Mandela Barnes has led his top primary rivals in fundraising, while also picking up high-profile endorsements from the likes of Rep. James Clyburn (D-S.C.) and Sen. Elizabeth Warren (D-Mass.).
Still, Wisconsin won't hold its primaries until August, leaving the nominating contest far from settled. Meanwhile, Johnson indicated last month that he will make a decision on his political future soon. If Johnson chooses to seek another term, he'll be the only GOP Senate incumbent to seek reelection in a state that Biden won in 2020.
Former Nevada state Attorney General Adam Laxalt is the likely GOP favorite to challenge Sen. Catherine Cortez Masto (D-Nev.) next year. He's already picked up the support of both Trump and McConnell, and has the benefit of already having run statewide, both successfully and unsuccessfully.
Democrats have been eager to cast Laxalt as a Trump acolyte who has backed the former president's false claim that the 2020 election was rigged. They're also quick to note that Laxalt lost his 2018 bid for the Nevada governor's mansion.
Still, there's little doubt that Nevada is in play for the GOP. Trump lost the state last year by only 2 points. At the same time, Republicans picked up some support among Latino voters in 2020, which could give Democrats a rockier path to victory next year.
Despite Trump's victories in the state in 2016 and 2020, North Carolina remains nearly evenly split between the two parties statewide. At the same time, Sen. Richard Burr's (R-N.C.) decision to retire after his current term expires in 2023 has created a classic battleground scenario.
While 2020 proved disappointing for North Carolina Democrats - Trump narrowly carried the state, while Sen. Thom Tillis (R-N.C.) beat Democrat Cal Cunningham in a hotly contested Senate race - the party is hoping to make a comeback in 2022, even in the face of national challenges for Democrats.
For now, the Republican primary field is mired in division. Trump has endorsed Rep. Ted Budd (R-N.C.) for the GOP Senate nomination, but former Gov. Pat McCrory is putting up a tough fight. Another GOP candidate, former Rep. Mark Walker (N.C.), is considering a possible run for the House instead, though he has said he will remain in the Senate contest for the time being.
Former state Supreme Court Chief Justice Cheri Beasley is the favorite to win the Democratic nomination. State Sen. Jeff Jackson exited the Democratic field earlier this month and threw his support behind Beasley.
Democrats, for the most part, have rallied around Rep. Tim Ryan (D-Ohio) as their choice to succeed retiring Sen. Rob Portman (R-Ohio) next year, seeing him as the kind of candidate capable of replicating the success of Sen. Sherrod Brown (Ohio), the last remaining statewide elected Democrat in Ohio.
In the Republican field meanwhile, the candidates have lurched to the right in an effort to capitalize on Trump's success in the state in 2016 and 2020.
The former president has yet to endorse in the contest, but that hasn't stopped several of the top candidates - including former state Treasurer Josh Mandel, entrepreneur and author JD Vance and former state GOP Chair Jane Timken - from fighting over their loyalty to Trump.
Still, Democrats have had a tough run in Ohio in recent years, leading some to question its status as a political battleground, and for now, it's still seen as leaning in the GOP's favor in 2022.
Republicans were dealt a blow last month when New Hampshire Gov. Chris Sununu announced that he would seek reelection next year instead of challenging Sen. Maggie Hassan (D-N.H.), denying Senate GOP leaders one of their top recruits of the 2022 elections.
Still, Republicans are bullish about their chances of ousting Hassan next year, even without Sununu in the race, arguing that she remains one of the most vulnerable Democratic Senate incumbents in the country. A University of New Hampshire poll conducted in October found Hassan's favorability underwater at 33 percent to 51 percent.
Nevertheless, Republicans have yet to coalesce around a single candidate to take her on. Another potential heavyweight contender, former Sen. Kelly Ayotte (R-N.H.), also announced in November that she would not run.
Rep. Val Demings (D-Fla.) has emerged as the leading candidate to take on Sen. Marco Rubio (R-Fla.), giving Florida Democrats a high-profile name on the ticket in 2022.
But beating Rubio isn't going to be an easy task. For one, Democrats have been dealt a series of stinging defeats in Florida in recent years, most recently in 2020 when Trump carried it by a more-than-3-point margin - a relative landslide by Sunshine State standards.
And for the first time in modern history, Republican registered voters now outnumber Democrats.
Still, Demings is a prolific fundraiser, raking in nearly $8.5 million in the third quarter of 2021 alone. And despite the GOP's newfound voter registration advantage, Republicans say they're taking the Senate race seriously, well aware of how expensive and unpredictable Florida can be.
Missouri has, for the most part, become safe territory for Republicans, handing Trump a 15-point win in the 2020 presidential election.
While there's a crowded field of Republicans seeking the nomination to succeed retiring Sen. Roy Blunt (R-Mo.) next year, many GOP operatives remain concerned that the state could become competitive for Democrats if disgraced former Gov. Eric Greitens wins the Republican nod.
Trump hasn't endorsed in the Senate race yet, though he hasn't ruled out the possibility of backing Greitens, who resigned from the governor's mansion in 2018 following an investigation into allegations of sexual and campaign misconduct.
There are still a handful of other Republicans seeking their party's nomination to succeed Blunt, including Missouri Attorney General Eric Schmitt and Reps. Vicky Hartzler (Mo.) and Billy Long (Mo.).
Democrats are also contending with a primary of their own. Who emerges from the two nominating contests could determine just how competitive the Senate race in Missouri will be.
--Updated on Dec. 27.