The Democrats are fending off a Republican offensive aimed at overturning their tiny majority in the Senate.
Retaking control of the US Congress’s upper chamber may represent the GOP’s best opportunity of success in November’s election, according to analysts, surpassing their chances of retaking the White House or even retaining control of the House of Representatives.
But with a burst of enthusiasm from Kamala Harris’s campaign, Democrats are still competitive.
What is the Senate’s current make-up?
The Democrats currently hold 48 of the 100-member chamber’s seats plus having the support of three independent senators who sit with the party’s caucus and back it on important votes. The Republicans have 49 seats, meaning they only need to gain two in November – when one-third of the seats are up for grabs – to regain control.
How likely are Republicans to take control?
On the face of it, the GOP have the edge. The retirement of Joe Manchin, a centrist Democrat from West Virginia with a track-record of taking Republican-friendly positions, is almost certain to result in a GOP gain in a state that has become a party stronghold.
If Donald Trump were to retake the White House, winning West Virginia alone would be enough to effectively hand the Senate to the Republicans, with the vice-president being awarded the casting vote under the US constitution in a 50-50 split scenario.
Related: Republicans hope for Senate majority after strong West Virginia primary result
Where are sitting Democrats most vulnerable?
Two Democratic incumbent senators in GOP heartland states are seen as particularly vulnerable; Jon Tester of Montana and Sherrod Brown of Ohio. The latter is a one-time election battleground that has been won by Trump in recent elections and is now considered solid Republican territory.
In states that have become increasingly conservative, both Tester and Brown have sought to stay competitive by emphasising their independence from the more liberal national party organisation. Each stayed away from last month’s Democratic national convention in Chicago to focus on wooing independent and swing voters whose support is deemed vital to holding their seats. The Cook Political Report has designated both contests as toss-ups.
Montana: John Tester v Tim Sheehy
Tester, who has held the seat since 2006, is running for a fourth term in a state Trump won by 16 points four years ago against Tim Sheehy, a former navy Seal and businessman, who has the former president’s backing.
Ohio: Sherrod Brown v Bernie Moreno
Brown has been in the Senate for as long as Tester and is also seeking his fourth term. His opponent, Bernie Moreno, is another Trump-backed candidate who was not the choice of the Republican establishment in Ohio.
Key presidential battleground states where the Republicans hope to make gains
Nevada: Jacky Rosen v Sam Brown
Jacky Rosen, a first-term senator elected in 2018, is facing a challenge from Sam Brown, a Republican with a bracing back story but a thin political resume. Brown, a graduate of West Point military academy and veteran of the long US-led military effort in Afghanistan, barely survived a roadside bomb attack in Kandahar that left him permanently scarred. Like Tester and Brown, Rosen opted to skip the recent Democratic convention to focus on her Senate defense.
The Cook Report categorizes the race as leaning Democrat.
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Wisconsin: Tammy Baldwin v Eric Hovde
The two-term senator Tammy Baldwin is up against Eric Hovde, a wealthy GOP banker and businessman who is funding his own campaign. But his local bona fides have been questioned by Democrats who have stressed his connections to southern California.
The race is also judged leaning Democrat column by the Cook Report.
Pennsylvania: Bob Casey v David McCormick
The three-term incumbent Democrat senator Bob Casey is pitted against David McCormick, former chief executive of Bridgewater Associates, one of the world’s largest hedge funds.
Casey is favoured to hang on to his seat, partly because of strong local name recognition. His opponent has already suffered defeat in a Pennsylvania Senate race, having narrowly lost the Republican state primary in 2022 to Mehmet Oz, who then went lost to Democrat John Fetterman in the election for a seat that had been left vacant by the retirement of a GOP incumbent, Pat Toomey, one of only seven Senate Republicans to vote to convict Trump over the January 6 attack on the US Capitol at his second impeachment trial.
The Cook Report classes it as leaning Democrat.
Arizona: Ruben Gallego v Kari Lake
A seat being left vacant by the retirement of Kyrsten Sinema, a former Democrat who quit the party to become an independent, is now a key target of Kari Lake, a one-time television news anchor who has positioned herself as a vocal Trump supporter and arch-exponent of the lie that the 2020 election was stolen. She repeated the tactic when she lost the 2022 Arizona governor’s race to Democrat Katie Hobbs. Her opponent is Gallego, a Democrat member of the House and former Marine veteran who served in Iraq.
The Cook Report judges the contest as leaning Democrat.
Michigan: Elissa Slotkin v Mike Rogers
Here the Republicans are on the offensive to replace a retiring Democratic senator, Debbie Stabenow, who is stepping down after 24 years. Trying to fill her shoes will be Elissa Slotkin, currently a Democrat member of the House, who will be in a race with Mike Rogers, a mainstream Republican who once said his party had to move beyond Trump before changing tack to embrace him, earning the former president’s endorsement.
The race is considered a toss-up by the Cook Report.
Maryland: Angela Alsobrooks v Larry Hogan
Solidly Democratic Maryland, which includes the liberal suburbs of Washington DC, is crucial to the party’s hopes of clinging to its Senate majority.
Instead, it’s turning into a dogfight between the Democratic candidate, Angela Alsobrooks, the executive of one of Maryland’s biggest countries, and the state’s former GOP governor, Larry Hogan. A recent American Association of Retired Persons poll showed the pair at 46% each – this despite Kamala Harris holding a near-20% state lead in the presidential race. Part of the explanation is the moderate public profile of Hogan, a traditional Republican who has positioned himself as an anti-Trump Republican and has said he does not seek the former president’s endorsement.
Indeed, buoyed by the recent poll, Hogan has now gone further, marketing himself in a fresh ad as one of the few Republicans who has never “caved” to Trump and extolling his decision to dispatch the Maryland national guard to put down the 6 January 2021 attack on the US Capitol.
As a result, a state that Trump lost to Joe Biden by 33 points in 2020 is in toss-up territory, according to the Cook Report.
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Possible dark horse races?
Florida: Where Republican incumbent Rick Scott is being challenged by Democrat Debbie Mucarsel-Powell.
Texas: Colin Allred, another Democrat, is trying to unseat the combative sitting senator, Ted Cruz, who ran unsuccessfully for the Republican presidential nomination in 2016.
The Cook Report assesses both races as likely Republican.
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