Trump also trails by a slim margin in three other states he won in 2016 -- Georgia, Iowa and Ohio, according to an average of state polls by the website RealClearPolitics (RCP)
The November 3 US presidential election is boiling down to a handful of key states that will decide the race between Democrat Joe Biden and President Donald Trump.
Trump carved a narrow path to victory in 2016 by winning the battleground states of Florida, Pennsylvania, Michigan, North Carolina, Wisconsin and Arizona.
This time polls have him behind in all six -- albeit by narrow margins in some.
Trump also trails by a slim margin in three other states he won in 2016 -- Georgia, Iowa and Ohio, according to an average of state polls by the website RealClearPolitics (RCP).
Here is a look at some of the key states:
Biden's birth state is the largest at play in the Rust Belt, a north-central region marked by decades of industrial decline.
Trump volunteers are swarming the state, including city suburbs where they are canvassing door-to-door.
On the Democratic side, former president Barack Obama is to make his first appearance on the campaign trail on Wednesday at an event in Philadelphia for his former vice president.
Pennsylvania's big cities will vote heavily for Biden, while its rural west and conservative central regions are committed to Trump. Its suburbs and northeast will be critical.
RCP average: Biden leads by 5.6 percentage points.
Michigan narrowly tipped for Trump in 2016 and is being fiercely contested this year.
Trump has visited the Great Lakes state to argue he is ushering in an American comeback, but voters are concerned about the coronavirus' impact on the economy and the president's response to the pandemic.
Democratic Governor Gretchen Whitmer has clashed repeatedly with the president and her enforced lockdowns have angered conservatives.
Gun-toting protestors staged demonstrations outside the state capitol this summer and members of a right-wing group were arrested recently for plotting to kidnap the governor.
RCP average: Biden leads by 7.2 percentage points.
Democrat Hillary Clinton opted against campaigning in America's dairy land in 2016, and voters punished her for it.
This year Democrats highlighted Wisconsin, locating their national convention there although the gathering moved online over coronavirus concerns.
Trump and Biden have campaigned in the state, while Vice President Mike Pence and Biden running mate Kamala Harris have also visited.
RCP average: Biden leads by 6.3 percentage points.
The largest of the swing states anchors the Sun Belt, the band of states across the US South and Southwest rapidly growing in population, and features agriculture, military industry and large numbers of retirees.
Republicans are mounting a fierce defense here, with Democrats accusing them of suppressing the vote, particularly in communities of color.
The state's huge Latino population will be key, and polls show them aligned with the Democratic ticket less than in 2016.
At the same time, polls show seniors swinging away from Trump because of his handling of the pandemic.
Most experts say Florida is a Trump firewall; if it's breached, Trump likely loses the White House.
RCP average: Biden leads by 1.4 percentage points.
This traditionally conservative state went to Trump by three points four years ago but both parties acknowledge it is now too close to call.
North Carolina's governor is a popular Democrat who has won praise for his balanced response to the pandemic.
Republicans based their national convention here, although it ended up being largely online.
RCP average: Biden leads by 2.7 percentage points.
Arizona has been a Republican stronghold for decades, but its electorate is changing, with a growing Latino community and an influx of more liberal Californians.
Conservative voters appreciate Trump's efforts to restrict immigration and build a wall on the border with Mexico.
But Trump has hurt his prospects by repeatedly denigrating the late senator John McCain, who represented Arizona and still looms large over its politics. McCain's widow, Cindy McCain, has endorsed Biden.
RCP average: Biden leads by 4.0 percentage points.
Trump won easily in Iowa four years ago, beating Clinton by nearly 10 points, but the race appears close this time in the midwestern farming state.
Trump held a campaign rally in Iowa last week, a sign he is playing defence in a state he had been expected to win.
RCP average: Biden leads by 1.2 percentage points.
A Democrat has not won a presidential race in Georgia since Bill Clinton in 1992 but it has been trending Democratic in recent years.
Trump held a rally in Georgia on Friday, an indication he may be on shaky ground there.
RCP average: Biden leads by 1.2 percentage points.
Ohio, with 18 electoral college votes, is a major prize.
Trump defeated Clinton in Ohio by 8.1 points but polls show a close race this time in the midwestern industrial state.
Biden has visited and touted his role in helping save the US automobile industry when he was vice president.
RCP average: Biden leads by 0.6 percentage points.