The battle for the Senate majority is on.
To do that, Democrats must gain a net pickup of four seats, or three seats plus the presidency.
The Senate map this year favours Democrats, who have made gains in several southern states experts would have never predicted just two years ago to be this close on the eve of the election.
The Cook Political Report rates nine GOP-held seats either as tossups are leaning towards the Democrats.
Five others are also in play.
The forecasting model at FiveThirtyEight predicts Democrats have a 77 per cent chance of wrestling back a majority.
Here are the seven key races that will decide control of the Senate:
1. Maine — Susan Collins (R)
Seeking a fifth term, Ms Collins is in the fight of her political life in a race that will provide valuable data on whether conservative moderates still have a seat at the table in national politics.
Ms Collins, who did not vote for Donald Trump in 2016, has refused to weigh in on the presidential election now that she is on the ballot with him.
“I’m not getting into presidential politics,” she said at her final debate with Maine Democratic House Speaker Sara Gideon.
Ms Collins has pitched herself as a bipartisan dealmaker who has stymied Republicans’ worst impulses on health care and as a firewall against a complete Democratic takeover of Washington, DC.
“What I don’t want to see is one-party control in Washington, because I think that would lead to a far-left agenda being pushed through the Congress.”
Ms Collins’ record in the Trump era reflects a senator who wants to appeal to a pragmatic middle that may no longer exist.
On the one hand, she cast a decisive vote in 2017 against the GOP’s bill that would have repealed Obamacare. On the other hand, she voted in favour of Republicans’ signature tax code overhaul that eliminated Obamacare’s individual mandate for American adults to buy health coverage, one of the health law’s main pillars that helped drive down premium costs for the most vulnerable Americans.
Ms Gideon has assailed the incumbent for voting to confirm Supreme Court Justice Brett Kavanaugh in 2018 amid a swirl of sexual assault allegations, and for voting to acquit Mr Trump on impeachment charges that he undermined US national security in Ukraine for his own political purposes.
Most election handicappers now rate the race either a Tossup or Tilts Democratic, but the polling margins have routinely fallen within the margins of error.
2. Arizona — Martha McSally (R)
An Election Night loss for the freshman Arizona Senator would spell an ignominious end to her political career.
Ms McSally was appointed by the state’s GOP Governor Doug Ducey to replace the late Senator John McCain. That was just months after she lost her 2018 Senate race to Democrat Kyrsten Sinema, producing a grab-bag of liberal taunts that she couldn’t win a Senate seat in Arizona so she had to call in political favours to obtain one.
Ms McSally’s Democratic opponent this time around, retired astronaut and gun control activist Mark Kelly, has dogged her for voting repeatedly during her four years in the US House to dismantle Obamacare, arguing the senator has abandoned the thousands of Arizonians with pre-existing medical conditions who rely on the 2010 health care law’s safeguards.
Mr Kelly has accused Ms McSally of spurning the maverick independence of her predecessor in the seat, Mr McCain, for naked partisanship and fealty to Mr Trump.
Both candidates have defended the late Mr McCain as a military “hero.”
The Cook Political Report rates Ms McSally’s race Leans Democratic. Mr Kelly has led the head-to-head horse race since launching his campaign last year, at times opening up a double-digit lead in the most reliable public polls.
The McSally-Kelly race has been one of the most expensive in the country, in a state that is also a presidential battleground.
Combined, the major-party nominees have raised $146m, according to Federal Election Commission statements.
3. Colorado — Cory Gardner (R)
The last time Mr Gardner and his Democratic opponent, John Hickenlooper, were on the same ballot in Colorado, they both won their respective races.
Mr Hickenlooper for a second term as governor, and Mr Gardner for the Senate seat the two are contesting now.
Their constituency has changed considerably in the six years since 2014, and not in ways that help Mr Gardner’s case for his own second term.
The Colorado Sun has reported that 250,000 voters have switched their registrations from Republican to Democratic in that time, and 500,000 new voters have registered. [https://www.coloradoan.com/story/news/2020/10/28/colorado-election-voters-have-changed-since-gardner-hickenlooper-last-ran/6055686002/]
Mr Gardner graduated from the House to the Senate in 2014 on a message of bipartisan cooperation on issues such as environmental protection, normalising the state’s budding marijuana industry, and a post-Obamacare solution to health care.
“What can we do to make sure we are protecting this beautiful environment?... What can we do to put more Colorado in Washington and less Washington in Colorado?” he said at a campaign stop in Boulder that year.
While he was one of the chief architects of a “once-in-a-generation” national parks conservation bill signed into law earlier this year — a big deal for a large, outdoorsy cut of the constituency in Colorado — Democrats say he has largely failed to live up to that cross-party billing.
Mr Gardner has voted for all three of Mr Trump’s Supreme Court nominees. He has repeatedly voted to repeal Obamacare and voted, like Ms Collins, for the same tax code overhaul overturning the health law’s individual mandate. He acquitted Mr Trump on impeachment. He has fallen in line with the rest of the Republican party’s rightward lurch on immigration.
Big-money conservative groups that run pro-Republican TV and digital ads have largely abandoned him, deeming the contest as a lost cause with several public polls showing him trailing Mr Hickenlooper by double-digit percentage points.
FiveThirtyEight’s projection model in the state shows Mr Hickenlooper winning 85 of 100 simulated contests.
4. Montana — Steve Daines (R)
One of the most fiercely politically independent states in America, Montana’s battleground status in the Senate this year is almost entirely attributable to the pan-ideological appeal of Democratic nominee Steve Bullock.
While Mr Bullock’s message of centrism flunked him out of the 2020 Democratic presidential primary, it’s a popular brand in his home state.
Case in point: The term-limited Montana governor won re-election in 2016 by 4 percentage points in the same year Mr Trump won the presidential vote there by more than 20 points over Hillary Clinton.
In Washington, Mr Daines, the first-term Republican incumbent, has billed himself as a “conservative conservationist” who was instrumental in lobbying Mr Trump to sign the bipartisan Great American Outdoors Act that Mr Gardner and other Big Sky lawmakers have touted.
But Mr Bullock has attacked Mr Daines for his previous hesitations to put conservation and tourism interests ahead of private development such as mining and oil drilling. That wishy-washiness is symbolised by Mr Daines support for a Trump appointee, never properly confirmed by the Senate, overseeing federal lands in the state who once declared his support for selling off government land to private companies.
The Cook Political Report has given the race a Tossup label, although FiveThirtyEight’s model gives Mr Daines a 65-35 advantage in its forecast model.
5. Alabama — Doug Jones (D)
Mr Jones defeated Republican Roy Moore in a 2017 special election by less than 22,000 out of more than 1.3m cast amid sweeping allegations that Mr Moore had acted inappropriately with underage girls as a lawyer in his 30s.
Democrats were euphoric about the victory in deep-red Alabama, but knew Mr Jones had just two years to build a record that could appeal to enough voters to earn a full term.
Mr Jones — a former federal prosecutor whose claim to fame is putting the white supremacist perpetrators of the infamous 1963 Birmingham church bombing behind bars decades later — has not been shy about his liberal voting record since joining the Senate.
He voted to convict Mr Trump on impeachment articles and has opposed both Justice Kavanaugh and Amy Coney Barrett’s Supreme Court nominations.
His staunch liberal record, despite hailing from one of the most conservative states in the country, has placed him in pole position to lead a President Joe Biden’s Justice Department as attorney general.
As for the Senate race, he’s facing former Auburn University head football coach Tommy Tuberville, who, unlike Mr Moore, is not credibly accused of diddling young girls.
In a state where Mr Trump is expected to beat Mr Biden by as many as 20 percentage points, that, along with being the GOP nominee, should be enough to carry him to victory.
6. South Carolina — Lindsey Graham
Ms Barrett’s Supreme Court confirmation battle may have provided a much-needed lifeline to Mr Graham’s re-election campaign to remind conservative-leaning, on-the-fence voters in South Carolina what the three-term incumbent can deliver them: conservative federal judges and justices.
Mr Graham has framed his race against Democratic nominee Jaime Harrison as a choice between “capitalism versus socialism,” “conservative judges versus liberal judges,” and “law and order versus chaos.”
Mr Harrison and Mr Biden are Trojan horses for a socialist agenda from left-wing radicals overtaking the more moderate Democratic establishment in Washington, Mr Graham and his conservative allies in the state have suggested.
When results trickle in on Election Night, we’ll see whether those tried-and-true GOP messaging strategies worked.
But so far they haven’t stopped Mr Harrison’s momentum in a state where three in 10 residents are black, like him.
Mr Harrison has made gains in the once ruby-red Palmetto State by branding Mr Graham a serial “flip-flopper,” on everything from his broken commitment not to seat a Supreme Court justice in a presidential election year to to his about-face embracing Mr Trump, who the senator called “a race-baiting, xenophobic, religious bigot” during the Republican presidential primaries in 2016.
The Democrat, who has set record-breaking fundraising totals this year, is tailoring his message to white independents and rural black voters weary of Mr Graham’s unwavering support for Mr Trump and struggles accessing affordable health care.
South Carolina is one of just 12 states that has refused the Obamacare offer to expand Medicaid benefits for low-income hospital patients. Mr Graham has voted to repeal Obamacare on countless occasions since it became law in Barack Obama’s second year in office.
A young resident physician at one of Mr Harrison’s recent drive-in campaign rallies told The Independent she sees diabetes patients every day who suffer directly from Mr Graham’s anti-Obamacare and anti-Medicaid positions.
FiveThirtyEight’s forecasting model spits out 77 victories for Mr Graham out of 100 simulations, but the Cook Political Report nevertheless rates the race a Tossup.
7. North Carolina — Thom Tillis (R)
An extramarital sexting scandal for the Democratic challenger, ex-state Senator Cal Cunningham, has cast a cloud of renewed uncertainty over this race that has long been considered one of the most competitive of the cycle.
If Mr Tillis, the Republican incumbent, had run more of a centrist campaign, perhaps the scandal would have sunk Mr Cunningham’s chances.
But he’s not a centrist.
The nonpartisan GovTrack tool places Mr Tillis among the more conservative half of GOP senators over the last two Congresses, voting with the president on more than 93 per cent of bills in that time.
Mr Trump beat Ms Clinton by 4 percentage points in the state that has been trending Democratic over the last decade, but the top-rated public polling outfits have consistently shown Mr Cunningham with a tight lead — within the margin of error — over the last several months.
The Cook Political Report and Inside Elections with Nathan L Gonzales both rate the race a Tossup.
Other key races
Both Georgia Senate seats are up Tossups, with GOP incumbents fighting off well-funded and highly organised Democrats who have surged in the final weeks.
Iowa GOP Senator Joni Ernst, a party loyalist, is in a Tossup race against Democrat Theresa Greenfield. The Hawkeye State is a smouldering battleground at all levels of the federal government: Mr Biden is looking to put it back in the Democratic column after Trump won there in 2016. And three of the state’s four congressional seats, currently held by Democrats, are up for grabs.
Democrats could spook GOP incumbents in Texas and Alaska and raise goosebumps in Kansas’ open-seat race.
Democratic Senator Gary Peters appears to have a firm handle on Michigan.