US election 2024: The demographic divides that will decide whether Trump or Harris becomes president

Let's talk about the big poll numbers and why - right now at least - they're sort of useless. But also sort of useful.

The Sky News poll tracker (always useful, whatever the current state of the race) is still showing a consistent lead for Harris. But because it's well within the margin of error, it doesn't tell us anything about who's likely to win the election.

What if we slice it differently and look at the swing states themselves? This is the latest polling.

Same problem here. Nevada has a healthy lead for Harris - perhaps beyond the margin of error. But the other six states are again within the margin of error so they could go either way. Especially North Carolina, which is a dead heat right now.

As our polling scores above are averages of several different polls, each with unique methodologies and sample sizes, it's hard to say exactly what the margin of error is likely to be - and it will almost certainly differ from state to state.

In 2020 the final national polls missed the result by 4.3 points, and by three points in 2016, but it was as high as seven in some key states. The error has tended to benefit the Democrats in recent elections, with final results better for Republicans.

Read more: Can we trust the polls for the US election?

And, because of the way the electoral college works, there's a scenario where everything actually hinges on North Carolina - a state that doesn't even show a lead for either candidate. It feels like we are flying blind.

But there's another way of slicing things, with demographics. This is a bit different to the way we look at demographics in the UK - they're the main point of interest in the exit polling, which doesn't publish a predicted overall winner like in a general election.

And there's good news for both candidates here, when you combine the different demographics with the swing states.

The demographic divides that favour Harris

One of the most significant dividing lines in American politics is race. Fewer than one in eight black voters backed Trump in 2020, compared with 87% who voted for Biden.

That split could be particularly important in the two battlegrounds in the south, Georgia and North Carolina, which have significantly higher black populations than the US average.

Hispanic and Latin American voters also tend to vote Democrat, although not quite as enthusiastically as black voters. They backed Biden over Trump by more than two to one in 2020, 65% to 32%.

These voters will be particularly important in Arizona and Nevada, close to the Mexican border.

Harris's standing in the polls among these groups is better than Biden's was before he dropped out, but it may still not reach the same levels as her Democrat predecessors (including Biden) in recent past elections.

But a big percentage is only helpful if it's out of a big number. The key for Harris will be persuading these voters to actually come out and cast their ballots.

Obama did this really well. Hillary Clinton didn't. Biden did a bit better than her. Harris now has less than three weeks to build the enthusiasm behind her campaign.

The ones that favour Trump

One group that does tend to back Trump is rural voters. And the battleground states in general have more rural voters than the US average.

Trump will likely still win among this group, but some polls show Harris performing better than Biden was.

Pennsylvania might be best known for its big cities of industry, but it's also powered by agriculture - only Texas and North Carolina are home to a higher overall number of rural voters.

You can easily spot the urban areas on this map of the 2020 results - Philadelphia in the far southwest, Pittsburgh in the east.

Winning in these crucial battleground states is never about winning across the entire state. It's all about maximising your wins in the areas you're likely to do best, while limiting your losses in the places your opponent is likely to win. No vote is worth any more than any other.

Back to the big poll number, then, and why it is sort of useful too.

If Harris adds to her national polling, that counts among black voters and women (two overlapping categories) within the rural voters within those swing states - which could be bad for Trump.

The rising tide of Harris's national polling raises the demographics that are very important in those seven swing states.

The Data and Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News. We gather, analyse and visualise data to tell data-driven stories. We combine traditional reporting skills with advanced analysis of satellite images, social media and other open source information. Through multimedia storytelling we aim to better explain the world while also showing how our journalism is done.