Control of the Senate in 2023 remains a toss-up race itself, as Democrats seek to expand their tiny majority and Republicans attempt to flip the chamber. 

After a primary season that was relatively kind to incumbent senators, campaigns and their allied outside groups have hit the final stretch of what may become the costliest midterm cycle to date.

All the senators running for reelection made it out of their primaries and will face voters in November in some of the nation’s most competitive contests. Democrats’ chances of retaining control improved over the summer after the Supreme Court’s decision overturning the federal right to an abortion. But Republicans still need only one more seat to take the majority in the chamber — currently at 50-50, with Vice President Kamala Harris breaking ties — and they expect inflation and economic concerns to drive voters toward their party despite flawed candidates in pivotal states. 

Democrats, from the most vulnerable in Nevada’s Catherine Cortez Masto on down to Washington’s Patty Murray, have made abortion rights a signature message in their campaigns. Republicans are not wavering in their attacks on inflation, crime and the economic malaise hanging over the country as it deals with the lingering effects of the coronavirus pandemic, supply chain disruptions and the global impact of Russia’s invasion of Ukraine. 

Though they’re not on the ballot, the 2020 presidential contenders cast a long shadow over the Senate races. Republican ads seek to link Democratic incumbents to President Joe Biden, while Democrats see a winning message in highlighting erroneous statements by GOP candidates — such as Don Bolduc in New Hampshire — that Donald Trump won the 2020 election.   

Unlike Roll Call’s House most vulnerable list, on which every member faces serious obstacles to reelection, the bottom of the Senate list includes members such as Murray, who are likely but not guaranteed to return to Capitol Hill in the next Congress. They are nevertheless worth noting because they have attracted challengers who are forcing them to run serious campaigns, intensifying the scramble for limited campaign resources that are already needed in the most hotly contested races.

Some of the most pivotal races — in places such as Pennsylvania, Ohio and North Carolina — are open seats, and because they don’t involve incumbents, they are not reflected on this list. 

Despite the many twists and turns over the past four months since our last update to the list, these are the same 10 senators identified in our previous version, though there are some changes to the rankings. 

Even as abortion has become a major messaging point for Cortez Masto’s campaign with the Supreme Court’s ruling overturning Roe v. Wade, the shift has done little, so far, to boost her standing in the polls, which have been showing sizable percentages of undecided voters. The state’s voters are familiar with her opponent, Republican Adam Laxalt, who served as Nevada attorney general. Having won statewide office previously, Laxalt appears a more polished candidate than some of his counterparts in other states. Cortez Masto held a campaign cash advantage on June 30, with $9.9 million to Laxalt’s $2.1 million.

Johnson’s favorability ratings have consistently declined since  2019. But Republican strategists maintain that Johnson is running a tight campaign, reflected in a Marquette Law School Poll released Wednesday that showed Johnson leading by 1 point over Lt. Gov. Mandela Barnes among likely voters after trailing for most of the summer. Johnson has put cash toward TV ads that focus on his work and family, while Republican outside groups are amplifying Barnes’ positions they believe will repel voters in a state Trump won in 2016. But Democrats are also planning to spend heavily on attacks on Johnson’s support of Jan. 6 conspiracy theories and recent proposals to change the mandatory spending status of Social Security and Medicare. 

Warnock hasn’t really stopped campaigning since he won one of two runoffs that gave Democrats the Senate majority in 2021. He has withstood GOP attacks depicting him as a radical socialist, and Republicans have transitioned to a strategy that acknowledges his “inspirational” life story but paints him as ineffective and too closely aligned with Biden. Republican Herschel Walker’s football fame has been overshadowed by campaign missteps and damaging personal revelations. But Walker enters the fall with a more disciplined message. Some recent polls showed him with a narrow lead, but another, released Wednesday, showed Warnock up by 6 points. The race could lead to another runoff. 

Kelly, like some of his fellow vulnerable Democrats, enjoys two crucial advantages: an eye-popping sum in his campaign account and a flawed opponent who emerged from a divisive and drawn-out primary. Kelly held nearly $25 million as of July 13, while Republican venture capitalist Blake Masters held $1.6 million. The National Republican Senatorial Committee and outside groups are likely to spend big in the race, though a super PAC tied to Senate Republican leadership may not, leading Masters to rely on ads funded by a candidate-specific super PAC that’s been largely funded to date by his primary patron, billionaire Peter Thiel.

Hassan caught a break last year when Gov. Chris Sununu declined to run for the Senate, and she may have caught another one this week when retired Army Brig. Gen. Don Bolduc won the Republican nomination over state Senate President Chuck Morse, who was establishment Republicans’ preferred candidate. Democrats think abortion could pull voters to their side despite Hassan’s low favorability rating, which was at 44-51 percent in a Saint Anselm College poll in August, compared with 46-49 percent in March. Republicans are still poised to spend heavily on the race, and Bolduc has a path to flipping this seat in a state where voters are known to be independent. 

Rubio has been overwhelmed on the airwaves by Rep. Val B. Demings, who has emerged as a fundraising juggernaut. Demings’ ads have played up a personal biography as a tough-on-crime former police chief, defusing one of the GOP’s most salient attacks in recent cycles, while hammering Rubio’s support for an abortion ban that would not include exceptions for rape and incest. But while the race has tightened — recent polls show Rubio leading by just a few points — Demings also has to contend with a state that has been increasingly leaning toward Republicans, with GOP Gov. Ron DeSantis potentially driving turnout in a race he is favored to win.

The GOP sees potential to regain ground in a state that has been tough terrain in recent years. Bennet has held his seat for 13 years — he was appointed in 2009 — and ran for president in 2020. Yet Republican strategists think he is enough of a blank slate that they can paint him as a D.C. elitist beholden to an unpopular president. GOP nominee Joe O’Dea, the owner of a construction company, does not dispute the 2020 election and supports some abortion rights. But the Dobbs ruling complicates Republican attempts to win independents in a state that passed a law in the spring codifying abortion rights — and which O’Dea notably opposed. 

Lee won his primary but faces a challenge in November from former Republican-turned-independent Evan McMullin, who made a long-shot presidential bid in 2016 in opposition to Trump. McMullin, a former Capitol Hill aide who has said he would caucus with neither party should he win, is banking on a coalition of support from a minority of GOP voters (about 38 percent backed someone else in the Republican primary), plus independents and Democrats, whose party did not field a candidate. Among Lee’s advantages in the race is his campaign cash, with $2.5 million on June 30 to McMullin’s $1.3 million.

Not only has Murray been up on the air with her own ads, but Women Vote!, the super PAC connected to EMILY’s List, also has invested $2.1 million in her reelection since late July. It may be an impossible feat for Republicans to overcome the state’s Democratic lean to oust Murray, but GOP operatives see potential in Tiffany Smiley, a first-time candidate and veterans advocate. Murray, who is seeking a sixth term, showed her electoral strength in an August all-party primary, in which she won more than 52 percent of the vote to Smiley’s almost 34 percent. Murray had $6.7 million in her campaign account on July 13, while Smiley held $2.3 million.

Murkowski demonstrated her crossover appeal in the Last Frontier’s August all-party primary, in which she finished first, with 45 percent of the vote. It was enough to quiet fears that she’s seriously vulnerable to fellow Republican Kelly Tshibaka, who has Trump’s endorsement. Murkowski, who voted for Trump’s impeachment, will face Tshibaka and Democrat Patricia Chesbro in a ranked voting election. The fourth candidate, Republican Buzz Kelley, said recently he was dropping out. He endorsed Tshibaka, but it’s unlikely to make much difference. Outside groups that had prepared to spend big for Murkowski have canceled their plans because they think she’ll prevail. The incumbent had $5.3 million on hand as of July 27, to Tshibaka’s $800,000.  

Niels Lesniewski contributed to this report.