Former US president Barack Obama has returned to the campaign trail, launching a stinging rebuke of Donald Trump with less than a fortnight before the Republican President’s election day face-off with Democratic nominee Joe Biden.

Mr Obama’s address at a drive-in rally in Philadelphia, Pennsylvania, was his strongest denunciation of Mr Trump yet.

“He hasn’t shown any interest in doing the work or helping anybody but himself,” Mr Obama said of Mr Trump on Wednesday (local time).

Mr Obama, who governed for two terms and remains one of the most popular figures in the Democratic Party, blasted Mr Trump for his handling of the coronavirus pandemic, noting the US President himself had fallen victim to the virus.

“Donald Trump isn’t suddenly going to protect all of us,” he said. “He can’t even take the basic steps to protect himself.”

“This is not a reality show. This is reality,” Mr Obama said in a nod to Mr Trump’s past as a reality TV host. “And the rest of us have had to live with the consequences of him proving himself incapable of taking the job seriously.

“I get that this President wants full credit for the economy he inherited and zero blame for the pandemic he ignored.

“But you know what? The job doesn’t work that way. Tweeting at the television doesn’t fix things. Making stuff up doesn’t make people’s lives better.”

Mr Obama’s appearance filled a gap left by Mr Biden, who has stayed at home in Delaware since Monday for meetings and preparation before his Thursday debate with Trump in Nashville, Tennessee.

Earlier in the day, Mr Obama spoke to black community leaders in Philadelphia.

“I’ve never lost hope over these last four years,” Mr Obama said. “I’ve been mad, I’ve been frustrated but I haven’t lost hope and the reason is because I never expected progress to move directly in a straight line.”

Americans are voting early at a record pace in 2020. There have already been 42 million ballots cast via mail and in person ahead of the November 3 election, amid concerns about the coronavirus and to make sure they will be counted.

Four years ago, Mr Obama took part in a rally in Philadelphia with then-Democratic nominee Hillary Clinton the day before the election, only to see Mr Trump narrowly take the state. The Biden campaign considers winning there a top priority.

In remarks at an evening rally in Gastonia, North Carolina, Mr Trump briefly mentioned Mr Obama, noting he had supported Clinton in her losing effort. “It was nobody who campaigned harder for Crooked Hillary than Obama, right?”

North Carolina is another battleground state where opinion polls show a tight race. Ms Harris was also in the state on Wednesday to mobilise voters in Asheville and Charlotte.

Mr Obama won North Carolina in 2008 but lost it in his 2012 campaign. Trump won it in 2016.

Mr Trump argued that coronavirus-related restrictions were harming the state’s economy and complained that Democrats and the news media were overly pre-occupied with the pandemic.

“All you hear is COVID, COVID,” the President said.

“That’s all they put on because they want to scare the hell out of everyone.”

Mr Biden’s running mate, Kamala Harris, was also in North Carolina to mobilise voters.

The last days of campaigning are taking place amid a surge in new cases of COVID-19 and hospitalisations in battleground states, including North Carolina and Pennsylvania but also Wisconsin, Ohio and Michigan. The virus has claimed the lives of more than 221,000 Americans.

Polling shows a majority of voters are disappointed in the way Mr Trump has handled the pandemic, which he has repeatedly said would disappear on its own.

Mr Biden and Mr Trump are scheduled to meet in their second and final debate on Thursday night (12pm Friday, AEDT), giving the Republican an opportunity to change the trajectory of a race that Mr Biden is leading in national polls.

Mr Biden believes he must win his birth state of Pennsylvania and has visited it more than any other state during the campaign. Mr Trump narrowly won the state over Democrat Hillary Clinton in 2016.

Mr Trump has gained ground there, according to a Reuters/Ipsos poll released on Monday, which showed the challenger leading by 49 per cent to 45 per cent, slightly narrower than a week earlier.

“If we win Pennsylvania, we win the whole thing,” Mr Trump said on Tuesday at a rally in Erie, in the state’s northwestern corner.

-with agencies