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 a knockout blow. 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 Senator 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
Trump’s approval is about 40% static
Donald Trump’s presidential approval ratings are at stable levels, according to the Telegraph monitoring poll.
The tracker, which takes an average of the last eight polls, estimates Mr. Trump’s approval rating at around 44%, while 54% disapprove of the way the president does his job.
The president’s approval ratings had picked up slightly recently, after experiencing a “rally around the flag” effect with Americans backing the government to deal with the coronavirus crisis.
The time since Donald Trump was elected has been rich in controversy and intrigue, but, underneath it all, few seem to have really changed their minds about America’s 45th President.