With minimal mail-in voting, the fate of Texas - and its 38 electoral college votes - is expected to be declared on November 3.
Should Mr Biden become the first Democrat presidential candidate to win the state since Jimmy Carter in 1976, Donald Trump's chances of retaining the Oval Office would have been dealt a fatal blow.
Influential Texas Democrats including former presidential candidate Beto O'Rourke have urged the party to pour resources into the state, arguing that victory would put Mr Biden on course for the White House on November 3 irrespective of results in Wisconsin, Pennsylvania, Michigan, Ohio, North Carolina, Arizona and Florida.
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Read more: 2020 live election polls tracker
Significantly 40 per cent of those surveyed have already cast their ballot, reflecting a nationwide trend which has seen a surge in early voting with people queueing for hours at polling stations across the country.
According to the latest figures, at least 56 million people have already voted - either by post or in person - because of the coronavirus pandemic which has claimed 225,000 lives in the US.
The surge in early voting suggests the US could be on course for a record turnout of around 150 million people - representing 65 per cent of the electorate, a proportion unseen since 1908.
Early voters included Mr Trump, who cast his ballot in Florida on Saturday at a library near his golf club in West Palm Beach.
With 29 electoral votes, Florida is another pivotal state in the election. Mr Trump, who won the state by 113,000 votes in 2016, is running neck and neck with Mr Biden this year according to the latest polls. However, the former vice president was 387,000 votes ahead on Saturday morning.
They are tied in Georgia and Mr Biden is narrowly ahead in North Carolina.
The former vice president will be hoping to reap the benefit of an advertising blitz, which has seen him spend $582.7 million (Â£446.9 million) on television slots - a new record for a presidential candidate.
Undeterred, Mr Trump, who defied expectations and the polls in 2016, is hurtling around the US making his case to voters in person.
Over the weekend the president held rallies in five states - North Carolina, Ohio, Wisconsin, New Hampshire and Maine. He will be on the road every day until the election with events planned for Pennsylvania on Monday before moving on to Michigan, Wisconsin, Nebraska and Nevada on Tuesday.
Mr Biden, who addressed a rally in Pennsylvania over the weekend, has been more cautious with in-person campaigning, arguing that he does not want to be responsible for "super spreader" events.
On Sunday Mr Biden and his running mate, Kamala Harris, held an "I will vote" concert with performances from an array of stars including Jon Bon Jovi, John Legend, the Foo Fighters and Cher.
Household names throwing their names behind the campaign included Helen Mirren and Whoopi Goldberg.
While Mr Trump has voiced optimism about his own electoral prospects, according to the Washington Post he told donors last week that he thought it would be tough for the Republicans to keep control of the Senate - partly because there are some candidates he does not wish to support.
He is on course to cement conservatives' grip on the Supreme Court with Amy Coney Barrett's nomination due to be confirmed by the Senate on Monday.
Mr Trump has been pushing hard for her nomination to go through rather than risk having a court, which could decide the fate of the election, deadlocked.
In the teeth of fierce Democratic opposition, the Republican-controlled Senate imposed a guillotine on Sunday. With former Republican rebel, Lisa Murkowski of Alaska, falling into line, Judge Barrett will become the sixth conservative member of the nine-strong court.