US presidential polls: Harris leads Trump nationally, but key swing state races tighter

But as Harris faces her first ever debate as a presidential nominee, there are signs that her upwards swing has hit a ceiling. Meanwhile, Trump will be hoping the debate offers his campaign a chance to recapture some momentum.

At the same time, the narrow geographical focus of the election is sharply coming into view, with the first ballots to determine the next occupant of the White House due to be mailed out to voters.

North Carolina had aimed to start mailing out its presidential ballots on Friday. But in what might be seen as a metaphor for the cliffhanging nature of the contest between Harris and Trump, what should have been standard protocol was delayed by a dispute over whether Robert F Kennedy Jr, hitherto running as an independent candidate, should have a place on the ballot.

Kennedy, who suspended his campaign on 23 August and endorsed Trump, is suing the North Carolina board of elections over its refusal to remove his name from the ballot in a state where surveys show the result on a knife edge.

The postponement added another layer of suspense to a contest that could not be tighter, according to fresh Guardian analysis of recent polls.

In a state with 16 electoral college votes up for grabs but where a Democratic presidential candidate has won only once since 1980, Trump and Harris are deadlocked at 48.07%.

The figures illustrate why Kennedy - who is trying to help Trump after concluding that his presence in the race was draining his support - is so keen to remove his name from the ballot.