Former US president Barack Obama has criticised Donald Trump and warned against complacency - despite favourable opinion polls - during his first public rally in support of Democratic challenger Joe Biden ahead of next month's presidential election.
At the drive-in rally in Philadelphia, Pennsylvania, one of a handful of battleground states expected to decide the election, Mr Obama lashed out at Mr Trump's behaviour and declared him "incapable of taking the job seriously".
But he also issued a stark reminder of 2016, when opinion polls showed Hillary Clinton as the clear favourite - only for her and her supporters to be shocked by a Trump victory on election day.
"We can't be complacent. I don't care about the polls," the former two-term president told the rally outside a baseball stadium.
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"There were a whole bunch of polls last time. Didn't work out. Because a whole bunch of folks stayed at home. And got lazy and complacent. Not this time. Not in this election."
He told supporters that too much was at stake to have four more years of Mr Trump leading the nation, seeking to contrast his successor - a Republican real estate mogul and ex-reality TV star - with his former vice president.
"This is not a reality show. This is reality," Mr Obama said.
"And the rest of us have had to live with the consequences of him proving himself incapable of taking the job seriously."
He pointed to Mr Trump's running roughshod over previous norms, including his re-tweets of conspiracy theories, and accused him of mishandling the US response to the coronavirus pandemic.
"Our democracy's not going to work if the people who are supposed to be our leaders lie every day and just make things up," he said.
"And we just become numb to it."
Earlier, at a roundtable with Black community organisers in Philadelphia, Mr Obama said "the pandemic would have been tough for any president, we haven't seen something like this for 100 years".
The coronavirus has killed over 220,000 people in the United States and seriously wounded the world's largest economy, prompting fierce criticism of the president's handling of the crisis.
"We can't afford another four years of this," Mr Obama said.
While Mr Obama was in Pennsylvania, Mr Trump visited North Carolina, another of the battleground states, where he riled up the crowd with popular campaign themes, such as his law-and-order platform.
"If Biden wins, the flag-burning demonstrators in the street will be running your federal government," Mr Trump told spectators gathered at a municipal airport in the city of Gastonia.
Mr Biden, 77, had no public events on his schedule for the third day in a row, leading 74-year-old Trump to accuse his Democratic opponent of going "into hiding".
The Biden campaign said he was preparing for the second and final debate against Mr Trump in Nashville, Tennessee, this evening.
Mr Obama remained on the sidelines during the Democratic presidential primaries, but he threw his support behind Mr Biden after his former vice president won the party nomination.
The Biden campaign is hoping the star power of the US's first Black president will help boost turnout among young voters and African Americans, who are key to Democratic hopes of recapturing the White House.
African Americans voted in record numbers for Mr Obama in 2008 and 2012 but their participation dropped off in 2016, a contributing factor to Mr Trump's victory over Ms Clinton.
