Control of the US Senate may be won by a narrow margin in Tuesday’s election, as Republicans fight to retain their majority against a surge of Democratic candidates confronting President Donald Trump’s allies across a vast political map.
Both parties see paths to victory and the outcome might not be known on election night.
From New England to the Deep South, the Midwest to the Mountain West, Republican senators are defending seats in states once considered to be tough territory for Democrats.
Washington’s handling of the coronavirus crisis, the economic effects it has caused and the nation’s uneasy mood are all critical issues for voters.
Record donations have flowed to Democrats from millions of Americans. Republicans are relying on deep-pocketed donors to try to shore up their senators.
Mr Trump and Democratic presidential nominee Joe Biden have aggressively aimed at states important to the Senate as they hit the final stretch of their campaigns.
Half the battle
Securing a Senate majority will be crucial for the winner of the presidency. Senators confirm administration nominees, including the Cabinet, and can drive or stall the White House agenda.
With Republicans now controlling the chamber 53-47, three or four seats will determine party control depending on who wins the presidency, because the vice president can break a tie.
“Let’s run through the tape,” said Senate Majority Leader Mitch McConnell, making a final campaign effort on Monday in Kentucky as he faces Democrat Amy McGrath, a former Marine fighter pilot.
Mr McConnell said he hoped to remain the Republican majority leader with Mr Trump as president.
But he acknowledged the tough Senate races could flip control to the Democrats.
Democrats have put Senate Republicans on the defensive deep into Trump country.
What started as a lopsided election cycle with Republicans defending 23 Senate seats, compared with 12 for Democrats, quickly became a referendum on the president and his party.
Some of the nation’s most high-profile senators are fighting for their political lives.
In South Carolina, Democrat Jaime Harrison is trying to topple Republican Lindsey Graham, one of the president's leading allies.
The two crossed the state in a rush of final campaigning, with Mr Graham acknowledging the tight contest after Mr Harrison by October raised $100 million, an unheard-of sum for the state.
The senator, making television appeals for cash, said he also hit the $100m mark at the weekend.
Stuck in Washington to confirm Mr Trump’s Supreme Court nominee Amy Coney Barrett a week before election day, senators quickly fanned out.
Some travelled alongside the president for last-ditch tours, often socially distanced in the pandemic, to shore up votes.
Thom Tillis, the Republican senator for North Carolina, joined Mr Trump’s rally in Fayetteville on Monday as he struggled to fend off Cal Cunningham, his Democratic challenger.
That was despite a scandal over texts Mr Cunningham sent to a public relations strategist.
In one of the most-watched races in the nation, Susan Collins, Republican senator for Maine, made a final campaign stop in Aroostook County near her home town, visiting workers in a sawmill.
Democratic challenger Sara Gideon met voters at the Whistle Stop Cafe for breakfast on Monday.
The Maine race is one of several that could push past election day if no candidate breaks the 50 per cent threshold.
Ms Collins has typically rallied support as an independently minded centrist, but the tight contest shows the difficulty Republican senators have appealing to Mr Trump’s most ardent backers, while also retaining support from more moderate voters.
Democrats have more than one route to secure the three or four seats needed to capture the majority in the Senate, and Republican strategists conceded the incumbents will almost certainly suffer defeats in some key races.
Younger voters and more minorities are pushing some states towards the Democrats.
In Colorado, the parties have essentially stopped spending money for or against Cory Gardner, the state's Republican senator, because it seems he is heading towards defeat by Democrat John Hickenlooper, a former governor.
Arizona could elect two Democratic senators for the first time since last century if former astronaut Mark Kelly maintains his advantage over Republican Martha McSally for the seat once held by the late Republican, John McCain.
Even the open seat in Kansas, which has not elected a Democrat to the Senate since 1932, is being contested.
“The better President Trump does in a state, the easier it is to win any race,” said Corry Bliss, a Republican strategist.
The biggest risks to Democrats come in Alabama and Michigan.
Republicans are expecting to reclaim the seat in Alabama, where Doug Jones, the state's Democratic senator, pulled off a rare 2017 special election win in the Trump stronghold.
But he now faces an uphill campaign against Republican Tommy Tuberville, a former Auburn football coach.
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Democratic presidential candidate Joe Biden speaks at a campaign canvassing event in Scranton. AP Photo -
President Donald Trump speaks to campaign workers at the RNC Annex in Arlington, Virginia. Bloomberg -
A member of the Fletcher Street Urban Riding Club rides a horse down 52nd Street to encourage people to vote in Philadelphia. Bloomberg -
A poll worker poses for a picture in the Entertainment and Sports Arena in Southeast Washington, DC. EPA -
A jogger carries a Vote! flag as he passes a polling station in San Antonio. AP -
Voters line up at the Trenton Town Hall during Election Day in Trenton, Wisconsin, U.S. Reuters -
A young boy waits for his father to cast his ballot at Greenwich High School in Greenwich, Connecticut. AFP -
Democratic presidential candidate, former Vice President Joe Biden, waves from the front steps of his childhood home, during an early visit on Election Day, in Scranton. AP Photo -
First lady Melania Trump arrives to vote at the Morton and Barbara Mandel Recreation Centre, in Palm Beach, Fla. AP Photo -
Voters wear face-coverings while waiting in line to vote for the 2020 US elections at the Los Angeles County Registrar in Norwalk, California. AFP -
The White House is seen at sunrise during the election day, in Washington. Reuters -
Voters queue at the Waterville Junior High School polling station before doors open on the election day in Waterville, Maine. Reuters -
Voters wait in line at a polling station on election day in Winchester, Virginia, early on Tuesday, November 3, 2020. AFP -
Selectman Les Otten drops a ballot in a box shortly after midnight for the US presidential election at the Hale House at Balsams Hotel in the hamlet of Dixville Notch, New Hampshire. Reuters -
A board shows results of ballots cast shortly after midnight for the US presidential election at the Hale House at Balsams Hotel in the hamlet of Dixville Notch, New Hampshire. Reuters -
A woman casts her vote at the Hazel Parker Playground on election day in Charleston. AFP -
An election official stands near the ballot boxes at Ballard High School in Louisville. AFP -
Voters wait in line to cast their ballots at John F. Kennedy Library in Miami, Florida. AFP -
Democratic presidential candidate Joe Biden departs on election day in Wilmington, Delaware. Reuters -
A volunteer with Democracy North Carolina sits to answer questions at Waddell Language Academy in Charlotte, North Carolina, shortly after the polls opened. AFP -
People wait in line to vote in Portland, Maine. AFP -
Voters wait in line to cast their ballots at the old Stone School, used as a polling station, on election day in Hillsboro, Virginia. AFP -
Voters wait in line adhering to distancing rule to cast their ballots on election day in Philadelphia, Pennsylvania. Reuters -
Poll manager Susan Taylor wears shoes with the word 'Vote' as she checks people in to vote at the Hazel Parker Playground on election day in Charleston. AFP -
Cookies representing the presidential candidates for sale at the Oakmont Bakery in Oakmont, Pennsylvania. AFP -
A person votes in a socially distanced space in Portland, Maine. AFP -
Democratic presidential candidate Joe Biden salutes as he leaves Scranton, Pennsylvania. AFP -
Democratic presidential candidate Joe Biden(R) visits Hanks Hoagies in Scranton, Pennsylvania. AFP -
Voters wait in a long line to cast their ballots at Church of the Servant in Oklahoma City, Oklahoma. Reuters -
Donovan Faison, a 27-year-old first-time voter, wears an unusual mask and sunglasses as he feeds his ballot into a tabulator machine after voting at a polling station during the election in Durham, Durham County, North Carolina. Reuters -
Voters mark their ballots at First Presbyterian Church on Election Day, in Stamford, Conn. AP Photo -
An election inspector checks the names of voters as the counting of ballots begins on Election Day at City Hall in Warren, Michigan., in Macomb County. AP Photo -
Voters line up before polls open on Election Day at a precinct in Warren, Michigan. AP Photo -
Erin Doherty hugs her mother Susanna Dew, 61, who is voting for the first time in her life, as they wait in line at a polling place on election day in the Mid City section of New Orleans. AP Photo -
Voters mark their ballots at Bloomfield United Methodist Church in Des Moines, Iowa. AFP
In the presidential battleground of Michigan, Republicans have made an aggressive push for John James, a black businessman, against Democratic Senator Gary Peters.
“We think the numbers are moving,” said Senate Leadership Fund President Steven Law.
But voter turnout during the coronavirus crisis remains vital, and volatile, after more Americans than before – about 100 million – cast early ballots.
Mr Biden and Mr Trump visited Georgia, where the state is reporting a boost in new voters.
Georgia’s two Senate seats are at stake and could well push to a January 5 run-off if no candidate reaches beyond the 50 per cent threshold.
David Perdue, a former business executive who Mr Trump calls his favourite senator, is working to fend off Democrat Jon Ossoff, another candidate who has benefited from the wave of donations.
Republican Senator Kelly Loeffler faces fellow Republican Doug Collins and Democrat Raphael Warnock, in a special election for the seat she was appointed to fill with the retirement of Republican Johnny Isakson.
It is expected to be a long count in races across the country.
The political landscape is quickly changing from six years ago, when most of these senators last faced voters.
It is a reminder of how sharply the political climate has shifted in the Trump era.
In Montana, Republican Senator Steve Daines is trying to brush back Democrat Steve Bullock, the governor, in a state where Mr Trump was popular.
Democrats created an opening by recruiting a well-known candidate in Mr Bullock, who also ran in the party’s primary for president.
Iowa Senator Joni Ernst is fighting for a second term against Democrat Theresa Greenfield.
Texas Senator John Cornyn faces an upstart Democrat, MJ Hegar, in the once solidly Republican state.
And in Alaska, Democratic newcomer Al Gross, a doctor, has broken state fund-raising records in part with viral campaign advertisements as he challenges Republican Senator Dan Sullivan.
