Control of the US Senate is at stake in the November 8th midterm elections, as Republicans need to pick up only one seat to win control of the 100-seat chamber, which would allow them to block much of President Joe Biden's agenda.
The chamber is currently split 50-50 between Republicans and Democrats, who maintain control thanks to Vice President Kamala Harris' tie-breaking vote. Democrats hope to expand their margin.
Here are eight races that could determine the outcome.
Pennsylvania
John Fetterman, the Democratic state lieutenant governor, flipped Pennsylvania's Senate seat, beating Mehmet Oz, a TV host and heart surgeon who was endorsed by former President Donald Trump.
The race appeared to tighten in recent days, particularly after a rocky debate performance from Fetterman, who was hampered by the lingering effects of a stroke he suffered in May.
Oz faced accusations of carpetbagging as a longtime New Jersey resident and said that "local politicians" should be involved in a woman's decision to have an abortion.
Ohio
Republican JD Vance, author of the memoir Hillbilly Elegy, has won Ohio's open Senate seat, defeating Democratic US House Representative Tim Ryan in a state that has trended Republican over the past decade.
Former President Donald Trump endorsed Vance, and tech billionaire Peter Thiel was a major donor to his campaign.
Vance's more controversial opinions - that he did not care what happened in Ukraine and claiming the Biden administration was purposely flooding the Midwest with fentanyl - and Trump's comment at a campaign rally that Vance "is kissing my ass" made the race more competitive than expected. National Republican groups spent heavily to shore up his prospects.
Ryan emphasised his blue-collar background, supporting domestic jobs and a $15 minimum wage as his key policy planks, and distanced himself from party's liberal wing.
Arizona
Democratic Senator Mark Kelly, a former astronaut and husband of former U.S. Representative Gabby Giffords, is facing Blake Masters, a Thiel-backed Republican. The state is a former right-wing stronghold where Democrats have made gains in recent elections - Biden won the state by 0.3 per cent in 2020. Masters has sought to distance himself from controversial comments suggesting Social Security should be privatised. He also recently deleted portions of his campaign website where he advocated for a total abortion ban.
Kelly has been a moderate Democrat in the Senate, pushing for lower prescription drug costs and at times criticising the Biden administration's response to asylum seekers at the southern border with Mexico.
Although Republicans initially pulled funding in the wake of Masters' struggles, the race - as with many others - has tightened in recent days.
Georgia
In what is expected to be one of the closest races of the cycle, freshman Democratic Senator Raphael Warnock is up against Herschel Walker, who is endorsed by Trump.
Walker is a former college football star who has been hampered by a series of scandals, including allegations of domestic violence. A vocal anti-abortion advocate, Walker's campaign was rocked by reports that he paid for multiple former girlfriends to have abortions in the past.
Warnock, who serves as pastor at the Atlanta church once led by Martin Luther King, Jr., won a surprise victory in a special election in early 2021, giving Democrats control of the U.S. Senate. If neither candidate gets 50 per cent of the vote, the race will go to a run-off in early December.
Nevada
Democrat Catherine Cortez Masto, the first Latina to serve in the Senate, is defending her seat against state Attorney General Adam Laxalt, a Republican who spearheaded his party's efforts to overturn Biden's victory there in the 2020 election.
Cortez Masto has emphasised abortion rights, while Laxalt has sought to harness voter concerns about rising prices - a pattern playing out in other states as well. The race has remained extremely close.
In a state where 30 per cent of the population is Latino, analysts are watching whether these voters will continue to drift toward Republicans or whether Democrats can reverse this trend.
New Hampshire
Republicans nominated Don Bolduc, a retired U.S. Army general who promoted Trump's lie that the 2020 election was stolen, to run against incumbent Democratic Senator Maggie Hassan.
The seat was considered a top opportunity for Republicans, but some of Bolduc's statements - including, saying the FBI should be abolished and espousing Covid-19 conspiracies - have made it difficult for him to win support beyond his right-wing base. Bolduc has attempted to moderate his positions since his primary win, disavowing election fraud claims and saying abortion should be decided by the states, but analysts say Hassan is favoured to hold the seat.
North Carolina
Republican U.S. House Representative Ted Budd faces former state Supreme Court judge Cheri Beasley for an open U.S. Senate seat in a relatively low-key race that has not drawn as much national attention.
Budd, a gun store owner, has emphasised bread-and-butter concerns like inflation to appeal to moderate voters. He has also backed a national ban on abortions after 15 weeks and has appeared at several rallies with Trump.
Beasley supports expanding access to affordable healthcare and taking action on climate change, but has said she would not be afraid to break with her party. North Carolina has been politically competitive for more than a decade, but Republicans have won most statewide contests and analysts give Budd the edge.
Wisconsin
Republican Senator Ron Johnson is running against Democrat Mandela Barnes, the state's lieutenant governor. Johnson's statements against Covid-19 vaccines and the 2020 election could make him vulnerable, but he has pulled off surprise victories in past elections.
Republicans argue Barnes is too radical for the state, pointing to his past support for progressive policies like Medicare for All and a 2018 photo in which he is holding a shirt that reads "Abolish ICE," an immigration enforcement agency. - Reuters
