Former President Barack Obama returned to the campaign trail on Wednesday, launching a blistering attack on Donald Trump with less than two weeks to go before the Republican president's Election Day face-off with Democratic nominee Joe Biden.

Speaking at a drive-in rally in Philadelphia on behalf of Biden, his former vice president, Obama offered his most pointed critique yet of his successor.

"He hasn't shown any interest in doing the work or helping anybody but himself," Obama said of Trump. 

Obama, who governed for two terms and remains one of the most popular figures in the Democratic Party, blasted Trump for his handling of the coronavirus pandemic, noting that the 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." Obama's appearance filled a gap left by Biden, who has stayed at home in Delaware since Monday for meetings and preparation ahead of his Thursday debate with Trump in Nashville, Tennessee.

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

"I've never lost hope over these last four years," 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 this year, with 42 million ballots cast both via mail and in person ahead of the November 3 election, on concerns about the coronavirus and to make sure their votes are counted.

The record early vote so far represents about 30 percent of the total ballots cast in 2016, according to the University of Florida's U.S. Elections Project.

While Obama was speaking, Trump headed to North Carolina, another battleground state where opinion polls show a tight race, for a rally in Gastonia on Wednesday evening. 

Biden's running mate, Kamala Harris, was also in North Carolina to mobilize voters in Asheville and Charlotte.

The last days of campaigning are taking place amid a surge in new cases of COVID-19 and hospitalizations in battleground states, including North Carolina and Pennsylvania but also Wisconsin, Ohio and Michigan.

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

(With input from Reuters)