The candidates argued over foreign policy, immigration and - after months of anti-racism protests - race relations, with Biden saying Trump was "one of the most racist presidents" in history.
"He pours fuel on every single racist fire," Biden said. "This guy has a dog whistle as big as a foghorn."
Trump responded by criticizing Biden's authorship of a 1994 crime bill that increased incarceration of minority defendants while asserting that he had done more for Black Americans than any president with the "possible" exception of Abraham Lincoln during the U.S. Civil War in the 1860s.
OIL IN SPOTLIGHT
During a segment on climate change, Biden said his environmental plan would "transition from the oil industry" in favor of renewable energy sources, prompting Trump to go on the attack.
"He is going to destroy the oil industry," Trump said. "Will you remember that, Texas? Will you remember that, Pennsylvania?"
Biden said he simply wanted to eliminate federal subsidies for oil companies, a point he reiterated to reporters following the debate. "We're not getting rid of fossil fuels for a long time," he said.
During the debate, Biden criticized Trump's effort to persuade the U.S. Supreme Court to invalidate the 2010 Affordable Care Act, the sweeping healthcare reform passed when Biden was vice president in President Barack Obama's administration.
"People deserve to have affordable healthcare, period," Biden said, noting that the law prevented insurance companies from denying coverage to people with pre-existing conditions.
Trump said he wanted to replace the ACA with something "much better" that would offer the same protections, even though the administration has yet to propose a comprehensive healthcare plan despite a promise to do so for years.
Relatively few voters have yet to make up their minds, and Trump's window to influence the outcome may be closing. A record 47 million Americans already have cast ballots, eclipsing total early voting from the 2016 election.
The contentious first debate, when the two men traded insults, was watched by at least 73 million viewers. Trump passed up another planned debate last week after it was switched to a virtual format following his Covid-19 diagnosis.