WAUKESHA, United States — An energised Joe Biden and Barack Obama on Saturday accused Donald Trump of a massive screw-up in his handling of the coronavirus, but the US president remained ebullient despite trailing in polls with 10 days to go until the election.

Trump plowed through three campaign rallies in one day, targeting separate battleground states as he sought to close the gap with Biden.

But the president’s efforts have been inescapably overshadowed by a grim reality: The US set a daily record for new COVID-19 cases for the second day in a row on Saturday, at nearly 89,000, with a further surge expected as cold weather arrives.

The virus has claimed more than 224,000 American lives, with no end in sight, and a majority of voters say Trump has handled the crisis poorly.

"That’s Donald Trump’s presidency,” Biden said on Saturday during a drive-in rally, one of two events in his native Pennsylvania, a critical swing state. He spoke from a stage decorated with bales of hay and Halloween pumpkins.

"Donald Trump said, and is still saying, we’re rounding the corner. It’s going away. We’re learning how to live with it.”

Biden added: "We’re not learning how to live with it. You’re asking us to learn how to die with it and it’s wrong.”

The Biden campaign also deployed a key surrogate, former president Barack Obama, who slammed the Trump administration’s COVID-19 response.

"The idea that somehow this White House has done anything but completely screw this thing up is nonsense,” Obama told supporters at a drive-in rally in Miami, Florida.

"Donald Trump isn’t suddenly going to protect all of us. He can’t even take the basic steps to protect himself,” Obama added, referring to Trump’s hospitalisation for COVID-19 three weeks ago.

Also slamming the president’s failure to denounce white supremacy, and the many times he has lied in public, among other issues, Obama called on supporters to vote for his former vice president.

"We can make things better... That’s what voting is about, not making things perfect, but making things better,” he said.

"If we vote up and down the ticket like never before, we will elect Joe Biden.”

‘I get it’ 

Trump shrugged off Obama’s criticism, saying on Twitter that the former president had only "47 people” at his event.

"No energy, but still better than Joe!” he quipped.

And he shrugged off polls which continue to show his Democratic rival Biden leading the race.

"They want to depress you,” he said of the political and media outlets reporting the numbers. "These polls are much better than four years ago.”

"This election is a choice between a Trump super-recovery and a Biden depression,” he told supporters under a hot sun in North Carolina, highlighting promises of a cure to COVID-19 and a rapid economic recovery.

Biden has a firm lead in national polls, and narrower leads in many battleground states like Florida that typically decide the winner of US presidential elections.

But Democrats are not about to forget the stunning upset Trump pulled off in 2016 when he defeated Hillary Clinton, and Biden worked to chip away at Trump supporters on Saturday.

"I understand why some people voted for Donald Trump, they believe they weren’t seen, or being respected or heard... I get it. But then he got elected, he immediately forgot the Forgotten Man,” he said at a second rally in Dallas, Pennsylvania.

"You know, you’ll be seen and you’re heard and respected by me... if elected president, there’ll be no red states or blue states, only the United States,” he said.

Trump’s current grueling travels aim to repeat his 2016 feat.

Earlier Saturday, Trump cast his own vote at a public library in Florida, telling reporters with a smile: "I voted for a guy named Trump.”

He thus became one of nearly 55 million Americans to cast early ballots in a year when the coronavirus has made in-person voting problematic.

Campaigning at a frenetic pace, Trump then hop-scotched from North Carolina to Ohio, and later to Wisconsin, where he doubled down on his optimism, repeating claims that the country is "rounding the turn” of the pandemic.

Referring to earlier comments by Biden warning of a "dark winter” with COVID-19, Trump said he thought his rival was "very dark”.

"They say you sound too optimistic,” he added of himself. "That’s right, because I love this country. We’re optimists... Our country next year will be greater than ever before.”