What do polls tell us about race for Pennsylvania?

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With less than four weeks left to go until election day, the race for the White House is as close as ever.

Nationally, Kamala Harris remains a couple of percentage points ahead of Donald Trump - a lead she has had since she entered the race at the end of July.

But the US election is won and lost in the handful of states where both candidates stand a chance of winning - those known as the swing states.

The biggest prize in the seven swing states in this election is Pennsylvania, because it has the highest number of electoral college votes on offer and therefore makes it easier for the winner to hit the required 270 votes to become president.

Election polls - Is Harris or Trump ahead?

So what do the polls tell us about who might win there?

Back in July, the polls were looking bleak for Democrats in Pennsylvania. Joe Biden’s numbers had taken a hit after his lacklustre performance in the first presidential debate and Trump’s lead over him had grown to more than four percentage points, as you can see in the chart below.

But when the Harris campaign got going, the Democrats’ fortunes quickly recovered. Once there had been enough polls to calculate an average, data from polling analysis website 538 found that Harris had established a small lead over her Republican rival.

She has held on to that lead ever since - but not by much. At the moment, the latest data puts Harris on 48% and Trump on 47.2% - one of the smallest leads in the swing states.

When the margins are that fine, it’s impossible to know who is really ahead - especially when every poll conducted in Pennsylvania will have a margin of error that means the numbers could be higher or lower.

If the polls are right and Pennsylvania is as close as they suggest, it shouldn’t be a big surprise.

When Trump won the state in 2016 - the first time a Republican had done so since George HW Bush in 1988 - he did it by just 44,000 votes. Four years later, Biden retook Pennsylvania by 80,000 votes out of nearly seven million cast.

For Harris, the importance of winning the state couldn’t be clearer - no Democrat has won the White House without winning Pennsylvania since 1948. But at the moment, the polls suggest the race will go right down to the wire.

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BBC Question Time comes to the US

the BBC’s flagship political debate programme heads to Pennsylvania on Thursday, 10 October
it comes from the National Constitution Center in Philadelphia, presented by Fiona Bruce and featuring a local audience
the panel includes the BBC's Anthony Zurcher, former Trump campaign adviser Bryan Lanza and commentator Mehdi Hasan
it will be streamed on BBC website from 16:00 EST (21:00 BST)
UK audiences can also watch on BBC One and iPlayer, global audiences on the BBC News channel