BBC
About 240 million people are eligible to vote in this year’s US election, but only a relatively small number of them are likely to settle the question of who becomes the next president.
Experts believe there are only a handful of states that could plausibly be won by either the Democratic candidate, probably Kamala Harris, or her Republican predecessor, Donald Trump.
Six of them - Arizona, Georgia, Michigan, Nevada, Pennsylvania and Wisconsin - could hold the key to who will take the White House.
So both parties are campaigning intensively to win over undecided voters in these states.
Arizona
Mr Biden gained the presidency in 2020 with the support of the Grand Canyon State, which narrowly voted to back a Democratic candidate for the first time since the 1990s.
This state borders Mexico for hundreds of miles, and has become a focal point of the nation’s immigration debate.
Border crossings have fallen in recent months from record highs which have made the issue near the top of voters' concerns.
Mr Trump has repeatedly attacked Ms Harris’s record on immigration, because she was given a role by Mr Biden in trying to ease the border crisis.
He has also vowed to carry out “the largest deportation operation” in US history if he regains the presidency.
Arizona has also hosted a bitter row over abortion access, after state Republicans attempted to reinstate a 160-year-old near-total ban on terminating pregnancies. It’s become an explosive issue nationwide since 2022 when the US Supreme Court overturned a landmark ruling that gave women the constitutional right to abortion.
Georgia
Our list of swing states closely matches the list of places in which Trump-backed Republican officials tried to thwart Mr Biden’s win in the 2020 election. In Georgia, alleged election interference has landed Mr Trump in one of his four criminal cases.
He and 18 others are accused of conspiring to overturn his narrow defeat to Mr Biden in the state. He denies any wrongdoing, and the case looks increasingly unlikely to be heard in court before the election.
At 33%, Georgia has one of the country’s highest proportions of African-Americans in its population, and it is believed that this demographic was instrumental in Mr Biden flipping the state in 2020.
Some disillusionment with Mr Biden had been reported among America’s black voters, but the Harris campaign hopes to animate this constituency.
Reuters
Michigan
The Great Lakes state has picked the winning presidential candidate in the last two elections. Despite backing Mr Biden in 2020, it has become symbolic of a nationwide backlash over the president’s support for Israel during that country’s war in Gaza.
During Michigan’s Democratic primary contest in February, more than 100,000 voters chose the “uncommitted” option on their ballots, after a campaign was mounted by activists who want the US government to halt its military aid to Israel.
Notably, Michigan has the country’s largest proportion of Arab-Americans - a demographic whose support for Mr Biden was in jeopardy. But Ms Harris has started her campaign with a harder tone on Israel than him and some Gaza protesters have told the BBC they are hopeful she will be more sympathetic to their cause.
Mr Trump has highlighted the state’s significance in his potential path to victory. Commenting on events in the Middle East, he has called on Israel to finish its campaign over Hamas in Gaza, but "get it over with fast”.
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Nevada
The Silver State has voted Democrat for the last several elections, but there are signs of a possible turnaround by the Republicans.
Recent averages published by poll-tracking firm 538 indicate that Mr Trump had been enjoying a healthy lead over Mr Biden.
But a Democratic candidate like Ms Harris with greater appeal to younger and more diverse voters could close the gap.
Both candidates are vying to win the state’s sizeable Latino population.
Despite the fact that the US economy has shown strong growth and jobs creation since Mr Biden took the presidency, the post-Covid recovery has been slower in Nevada than elsewhere.
At 5.1%, the state has the highest unemployment rate in the country, after California and the District of Columbia, according to the latest US government statistics.
If Mr Trump wins power again, he has vowed a return to an agenda of lower taxes across the board, and fewer regulations.
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Pennsylvania
Pennsylvanians are far from unique among Americans for feeling cost-of-living pressures as a result of inflation. But the price of groceries has risen faster in their state than in any other, according to market intelligence provider Datasembly.
The BBC recently reported on how people were struggling to cope in Erie - a bellwether county for the rest of Pennsylvania, where as many as one in eight people are considered “food insecure”.
The state proved pivotal in the 2020 election, backing Mr Biden in his successful White House bid. He has a deep emotional connection to the working-class city of Scranton, where he grew up.
High inflation could hurt Ms Harris across the US as polling suggests it is giving voters an unfavorable view of the economy.
Mr Trump has sought to attack his new adversary by pinning her to the Biden economy.
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Wisconsin
The Badger State also picked the winning presidential candidate in both 2016 and 2020, by a margin of little more than 20,000 votes each time.
Pundits have suggested it is in marginal states like these where an impact could be made by third-party candidates who are campaigning against the policies of the big two candidates.
Polling has indicated that a sizeable show of support for an independent such as Robert F Kennedy Jr - who is fighting to get on the ballot in Wisconsin and other states - could harm the vote tallies for Ms Harris or Mr Trump.
Mr Trump has described that state as “really important… if we win Wisconsin, we win the whole thing”. The summer Republican National Convention will be held in the city of Milwaukee.
Ms Harris chose Milwaukee to host her first rally after entering the race.
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More on the US election
- SIMPLE GUIDE: Everything you need to know about the vote
- ANALYSIS: Three ways Trump will try to end Harris honeymoon
- SWING STATES: Where the election could be won and lost
- EXPLAINER: RFK Jr and others running for president
- VOTERS: US workers in debt to buy groceries
Georgia
Wisconsin
Nevada
Michigan
Pennsylvania
United States
Arizona