The presidential debates are a political version of the gladiatorial fight and have in the past circumvented the elections.
There are three debates before each election. The first debate in 2016 was watched by a record 84 million people on television.
This does not include the millions of people who watched on Facebook, YouTube, and other places online, or at parties and bars.
For many, it was the only time they listened at length to the candidates.
Polls four years ago showed he was reasonably close between Mr Trump and Hillary Clinton, with neither delivering the coup de grace. This time Mr. Trump sees a chance to wipe out his poll deficit in one evening.
Meanwhile, Mr. Trump and Mr. Biden’s roommates – Mike Pence and Sen. Kamala Harris – clashed in their own vice-presidential debate on Wednesday evening, with the focus dominated by the Covid-19 response from the Trump administration.
Read more: Analysis of the vice-presidential debate
What happened in the town halls?
Following the cancellation of the second presidential debate, the two candidates presented themselves in separate live town halls which were broadcast at the same time.
Mr Trump has made headlines after refusing to expose QAnon’s conspiracy theory, which falsely claims the US government is controlled by a “deep state” cabal of anti-Trump Satanist pedophiles. He said, “So I don’t know anything about QAnon. I know very little. What I hear is that they are very strongly against pedophilia. I agree with that.”
The president was asked about his decision to retweet a false conspiracy theory, from a Twitter account linked to QAnon, suggesting that the Navy Seals killed a duplicate of Osama bin Laden’s body, and that the Obama administration concealed it. Mr Trump said he was “just putting that out there” and “people can decide for themselves.”
Mr. Trump also denied being told in the Oval Office, by his national security adviser in January, that the coronavirus would be the greatest national security threat during his presidency.
In Philadelphia, Mr Biden said, “We’re in a situation where we have over 210,000 dead and what is he doing? Nothing. He’s still not wearing masks.”
Mr Biden put on his mask as he left the stage to be closer to the questioners.