Senate elections typically happen only every two years -- except sometimes they're three years in a row.
Democrats picked up two seats in November 2020. They won two more in Georgia runoffs in January 2021. And in 2022, they'll be fighting to keep control of the evenly divided chamber, where Vice President Kamala Harris is the tie-breaking vote.
But the fight for control is already center stage, since Congress -- and the 50-50 Senate, in particular -- helps shape how successful President Joe Biden will be in enacting his agenda. Democrats are eager to grow their majority so they can pass legislation with a more comfortable margin, while Republicans want the Senate back so they can check the Biden White House.
History is on Republicans' side. The party that loses the presidency usually gains seats in the midterm elections. By the numbers, at least, Republicans are more on defense heading into 2022: Of the 34 Senate seats up next year, Republicans are defending 20 to Democrats' 14. Not all of those are competitive, though: Only eight seats are currently rated as "battlegrounds" by Inside Elections with Nathan L. Gonzales.
The seat most likely to flip partisan control next fall, according to CNN's inaugural ranking, is in Pennsylvania, currently held by GOP Rep. Pat Toomey, who's not running for reelection. The top 10 Senate seats most likely to flip are based on CNN's reporting, as well as historical data about how states and candidates have performed. As the cycle heats up, polling, fundraising and advertising spending data will also become factors.
In this first edition, the top 10 slots happen to be evenly divided between GOP-held and Democratic-held seats. Three open seats are on the list, all currently held by Republicans who are retiring, making their seats more competitive than they otherwise would have been.
Regardless of historical precedent, the map of seats at play is important to consider. In 2018, for example, Democrats won the House by capitalizing on anti-President Donald Trump energy in the suburbs two years after he had been elected. But the Senate was a different story: Republicans gained seats because Democratic senators were up for reelection in rural red states where Trump had won.
This cycle, only one senator is running for reelection in a state carried by the opposite party's 2020 presidential candidate: GOP Sen. Ron Johnson. His Wisconsin seat is the third most likely to flip, but the two-term senator is the most vulnerable Republican incumbent.
Some states on this list will feel familiar. It wasn't too long ago that Georgia was the epicenter of the political universe, helping to deliver the White House and the Senate to Democrats. Expect the Peach State to be a big player again in 2022, with Democratic Sen. Raphael Warnock running for a full six-year term and control of the Senate on the line once more. Among the other states that were hotly contested in the 2020 cycle and again are on this list are Arizona, North Carolina and Colorado.
But long before the "Magic Wall" is coded in shades of red and blue, intra-party battles will dominate much of the news in 2021, with next year's nominating contests going a long way toward determining how competitive some of these general elections will ultimately be. Senate primaries -- the fields nascent as they may be -- are emerging as early indicators of where each party's base is headed. That's especially true for Republicans, who are very publicly grappling with what the GOP looks like with Trump out of the White House.
The former President may have left Washington -- and in unorthodox fashion, as the first President to ever be impeached twice -- but the control he has over the Republican Party was on display at the annual Conservative Political Action Conference in Orlando this past weekend. It was all about him -- gold statue and all. And even if his winning percentage in the unscientific straw poll wasn't commanding (55%), the rhetoric his acolytes and other 2024 prospects used was a nod to "Trumpism" -- a noun that the former President delighted in defining onstage in his first public remarks since leaving the White House.
Listing every Republican who voted to impeach him in the House or convict him in the Senate, Trump is targeting them for removal by challengers more loyal to him. He recently endorsed a former aide who's running against one of those House Republicans, and as he considers launching a super PAC, he's signaling he may be investing in additional races with more than just endorsements.
The extent to which Trump will get involved and will back candidates at odds with Senate GOP leadership remains to be seen. But he could be a potent factor in open-seat Senate races, like those in Pennsylvania, Ohio and North Carolina, where GOP incumbents -- two of whom voted to convict him -- are not seeking reelection.
Sen. Lisa Murkowski of Alaska is the only Republican senator who voted to convict Trump who's running for reelection next year, but he'd threatened her even before that vote. And the moderate Republican proved in 2010 that she can lose a primary (and GOP leadership's support) and still win the general election as a write-in candidate. Senate Minority Leader Mitch McConnell pledged on Monday that national Republicans will stand by her. Also working in Murkowski's favor this cycle may be a new "top four" system in the state, where all candidates run together in a nonpartisan primary and the four top finishers advance to the general election, where voters rank their preferences. For all those reasons, Alaska doesn't come close to cracking this list of seats most likely to flip, despite Trump's threats to Murkowski.
A few other GOP-held states could eventually earn honorable mentions. For now, the only chance that Iowa becomes competitive is if the 87-year-old Sen. Chuck Grassley retires. He hasn't said what he's doing yet. But even Joni Ernst, the state's junior GOP senator, who was in a top-targeted seat last year, won reelection by more than 6 points.
Similarly, Missouri looks to have become more solidly red since GOP Sen. Roy Blunt defeated Democrat Jason Kander by less than 3 points in 2016, which was a presidential year. One of his first Democratic challengers launched his campaign this year by mostly criticizing the other Missouri senator (Josh Hawley, who objected to the certification of Biden's electoral win) and trying to tie Blunt to him.