O'Malley reportedly said she thinks the Biden-Harris ticket has secured Arizona, a state that has voted red in every presidential race since 1996.
Spicing his stump speech with lurid exaggerations, Trump claimed that the "Biden family is a criminal enterprise".
"It's time we sent a message to these wealthy liberal hypocrites", he told the cheering crowd in Macon, Georgia on Friday night.
"I shouldn't joke because you know what?" AdvertisementThe New York Times reported that Trump is trailing behind Biden in polls as well as in campaign contributions.
Trump said he wasn't planning to raise any more money.
"Look. Everybody knows who Donald Trump is, let's show them who we are", Biden said at a auto rally in Detroit.
Ex-President Barack Obama has recorded videos in support of his former vice-president and spoken by video link at the Democratic National Convention in August, but has not yet appeared at a live rally in support of Joe Biden.
"We choose hope over fear, unity over division, science over fiction and yes, truth over lies". "Those are inflated national public polling numbers".
According to the latest Opinium/Guardian poll Mr Biden is now leading the race by 17 points.
While surprising perhaps to both campaigns and many political commentators, Biden's ratings strength has been intensifying for months as he deepens his lead in national polls - much to the chagrin of the ratings-obsessed Trump.
As the polling clouds darken for Mr Trump, prominent members of his own Republican party - including Senator Ben Sasse of Nebraska and Senator Ted Cruz of Texas - are sounding the alarm.
If we were to move our town hall with President Trump to a later timeslot we would be violating our commitment to offer both campaigns access to the same audience and the same forum. "He's got the character and the experience to make us a better country", he said.
They had been scheduled to hold one this Thursday but Mr Trump backed out after it was changed to a virtual debate following his COVID-19 diagnosis.
Biden's 90-minute session on ABC was watched by 13.9 million viewers, while Trump's hour-long event, which aired on NBC, as well as MSNBC and CNBC, brought in 13.1 million viewers across the networks combined. The candidates held rival town hall events instead.