Control of the United States Senate will be at stake when Americans vote on November 3.
Republicans presently hold a 53-47 majority over Democrats and two independents in the 100-member upper chamber of the US Congress. But Democrats are eyeing several paths to a majority through at least nine vulnerable Republican seats.
Democrats will need to pick up a net of four seats for a 51-49 majority. If they net only three seats to make it a 50-50 Senate, Joe Biden would also need to win the presidency for Democrats to seize the majority, as the vice president, Kamala Harris in his case, would hold the tie-breaking vote.
Indeed, Republicans are in a real battle with Democrats for control of the Senate, with Republican leader Mitch McConnell calling his party’s chances of keeping its majority as “a 50-50 proposition”.
The Senate plays an outsize role in passing federal laws and shapes the US presidency through its “advice and consent” role under the US constitution.
President Donald Trump has enjoyed a Republican majority in the Senate since taking office in 2017.
In February, the chamber acquitted Trump of abuse of power and obstruction of Congress after the House impeached him at the end of 2019.
Under Trump, the Senate has confirmed three conservative US Supreme Court justices and a deluge of conservative lower-court judges who will shape the US justice system for years to come.
And the Republican Senate has protected Trump from congressional attempts to reverse his executive actions and blocked legislative proposals by Democrats who control the 435-member US House of Representatives.
Thirty-five Senate seats, 23 held by Republicans and 12 by Democrats, will be up for election in November.
Here is a look at the top 10 most competitive races that could reshape the Senate:
Martha McSally, 54, is a retired US Air Force colonel and was the first female fighter pilot to fly in combat and the first to lead a fighter squadron in combat.
She served in the House of Representatives before running for the Senate in 2018, losing to Democratic opponent Kyrsten Sinema. However, McSally was appointed by Arizona’s governor, per state law, to take the seat of retiring Senator Jon Kyl, a Republican who had been named a placeholder following the death of Senator John McCain in 2018.
McSally faces a tough special election fight against challenger Democrat Mark Kelly, 56, a retired US Navy pilot and astronaut who is the husband of former US Representative Gabrielle Giffords, a gun-control advocate wounded in an attempted assassination in 2011.
McSally has tied herself closely to Trump, who feuded with McCain and disparaged him following his death from brain cancer. Polls show Kelly leading McSally, and he has raised more in financial contributions than she has.
Senator Cory Gardner, 46, who is serving his first term in the Senate, is considered one of the most vulnerable incumbents and is one of two Senate Republicans up for re-election in states that Trump lost in 2016.
Hillary Clinton won the state by 48 percent to 43 percent over Trump. Colorado Democrats have won the last four statewide races for governor. And Democratic presidential contender Joe Biden is leading Trump in Colorado polls.
Gardner, a lawyer and former US representative, has aligned himself closely with Trump, which analysts have suggested may hurt him in the increasingly Democratic state. He is set to face former Colorado Governor John Hickenlooper, 68, who dropped out of the Democratic presidential contest to run for Senate.
Hickenlooper leads Gardner in surveys, as independent voters in the state side with Democrats, and he has matched the incumbent in fundraising.
Gardner’s vulnerability has made him one of the closest-watched senators as Republicans move to confirm a Supreme Court nominee before the election.
David Perdue, 70, a businessman and close Trump ally, will seek a second term in November. Perdue, who is a cousin of Trump’s Secretary of Agriculture, former Georgia Governor Sonny Perdue, had never previously held elected office.
He faces 33-year-old media executive Jon Ossoff, who was endorsed by the late civil rights icon and US Representative John Lewis. Ossoff, who has never held elected office, gained name recognition in Georgia in 2017 during a failed bid to beat Republican Karen Handel for an Atlanta-area House seat.
Perdue had been leading in polls and fundraising, but recent surveys indicate support is moving towards Ossoff.
In an election fluke caused by the retirement of former Republican Senator Johnny Isakson, both of Georgia’s US Senate seats are up for grabs on Tuesday.
Republican Senator Kelly Loeffler, who was appointed as Isakson’s replacement last year, is running in a multi-party, multi-candidate “jungle primary” special election, featuring a powerful Republican opponent, Representative Doug Collins.
The contest is widely expected to end in a January run-off election. But as Loeffler and Collins battle each other for Republican votes, Democrat Raphael Warnock leads in the polls and had more cash on hand than either Republican as the race entered its final weeks.
Joni Ernst, 50, an Army National Guard lieutenant colonel and the first woman to represent Iowa in Congress, is running for a second term in the Senate.
She faces Democrat Theresa Greenfield, 56, a real estate developer who has turned Ernst’s anti-Washington establishment platform against her.
Trump carried Iowa by nine points in 2016, but recent polls in the state indicate slipping support for Republicans. Democratic donors poured cash into Greenfield’s campaign and outside groups have spent millions opposing Ernst.
Susan Collins, 67, is one of the most endangered Republicans in the US Senate. As the national Republican Party has moved to the right in recent years, Collins has struggled to maintain her position as a moderate. Now, she is the only Republican serving in Congress from the increasingly Democratic region of New England.
After Supreme Court Justice Ruth Bader Ginsburg’s death in September, Collins was the first Republican senator to break from party ranks and oppose moving forward with a replacement before the election. Collins ultimately voted against the confirmation of Amy Coney Barrett to the Supreme Court.
Prior to that, Collins had criticised Trump on occasion, but was unwilling to break from the party and vote against Trump in the Senate impeachment trial, and was a key enabler of the 2018 Senate confirmation of Trump’s conservative Supreme Court nominee, Justice Brett Kavanaugh.
Collins’s endorsement of Kavanaugh made her a target for Democrats, pro-choice advocates and women’s groups. Planned Parenthood, a reproductive health organisation that had previously supported Collins, endorsed her challenger, Democrat Sara Gideon, 48, who has gotten a big boost in funding from outside groups.
Gideon is well-known in Maine as speaker of the state House of Representatives and leads Collins in opinion polls.
Steve Daines, 58, who previously served in the US House of Representatives, is running for a second term in the Senate. He faces Montana’s Democratic governor Steve Bullock, who has garnered high approval ratings in the state.
Bullock, 54, joined the Senate race after abandoning a long-shot presidential bid, and was recruited by both former President Barack Obama and Senate Minority Leader Chuck Schumer.
While Trump handily won Montana in 2016, polls show Daines with only a slight edge over Bullock and independent analysts rate the race a toss-up.
Both candidates have shattered fundraising records for the state, with Daines bringing in $13m and Bullock $11m as of the end of June.
Thom Tillis, 60, a former speaker of the North Carolina House of Representatives, is running for his second term against Democratic challenger Cal Cunningham, a former state senator and Iraq war veteran.
Early on, Tillis had questioned some of Trump’s decisions, including his emergency declaration to build a wall along the southern border with Mexico. But he became one of the president’s strongest defenders during the Senate impeachment trial.
The race blew up into one of the most dramatic in the country when Cunningham’s candidacy was tripped up by a sex scandal after he holding a significant polling lead for months. His double-digit lead dwindled throughout October.
Trump has strong support among rural voters in North Carolina, as he does throughout the US South, and Tillis’s campaign is betting Trump will help win over swing voters on the economy and immigration.
Senator Lindsey Graham, one of Trump’s closest allies in Congress, was last re-elected to the Senate in 2014 with more than 55 percent of the vote. But this year, he is favoured to win by only a small margin against Democrat Jaime Harrison, who is running a powerful campaign backed by staggering fundraising numbers.
Recent polls show Graham with a slight lead over Harrison, based partly on his role in overseeing Barrett’s confirmation. Once a Trump critic, Graham faces scepticism among conservatives over his recent conversion to Trump ally, while the loss of his former maverick persona has disappointed moderates, analysts say.
Some polling evidence suggests Graham’s stewardship, as chairman of the Senate Judiciary Committee, of Amy Coney Barrett’s Supreme Court confirmation has helped him late in the campaign.
Doug Jones is the most vulnerable Democrat up for re-election in the Senate. He won office in 2018 in Republican Alabama in a special election contest against former Alabama Supreme Court Justice Roy Moore, whose candidacy was crippled by sexual misconduct allegations.
Jones now faces a more formidable foe in Tommy Tuberville, 66, a former big-time US football coach who led Auburn University to legendary victories over in-state rival University of Alabama six times between 1999 and 2008.
While Tuberville leads in polls, Jones has out-fundraised him by a wide margin. Independent analysts see the race leaning Republican.
Gary Peters, 61, is running for a second term against Republican challenger John James, 39, a Detroit businessman and a former helicopter pilot in Iraq.
James, an African American who has spoken about his interactions with police, has shown himself to be a formidable fundraiser running on a platform of unity and bipartisanship.
Peters faced criticism in the battleground state for his vote to convict Trump on articles of impeachment.
Peters leads slightly in polling and spending by outside groups. Analysts give him an edge to win in November.