1 MESSY AFFAIR
Tuesday night was less a debate and more a spectacle. United States President Donald Trump, 74, did the lion's share of interruptions, frequently talking over his opponent Joe Biden, 77, and heckling him.
Mr Biden, who often could barely get a word in, was occasionally thrown off balance. "Will you shut up, man?" he said at one point. "This is so unpresidential... keep yapping, man."
This would have played differently to different audiences. Mr Trump's supporters are likely to see him as strong and Mr Biden as a weak opponent who needed the moderator to stand up for him. Meanwhile, the President's detractors will call him a bully.
Mr Biden's strategy of addressing the camera at times, directly asking the audience whether their life experience contradicted the miraculous pandemic recovery extolled by Mr Trump, was very much in line with his brand of campaigning and folksy charm.
All in all, the barrage of interruptions meant the two men could hardly engage with each other on substantive points nor delve deep into policy discussions.
2 THE SPECTRE OF SOCIALISM
Mr Trump tried to paint Mr Biden as a socialist, while trying to pit the left wing of the Democratic Party against Mr Biden for not being leftist enough for them.
"They're going to dominate you, Joe, you know that," said Mr Trump. "Your party wants to go socialist."
"I'm the Democratic Party right now," Mr Biden said.
The former vice-president responded in a consistently moderate manner. Over the course of the debate, he explicitly said he was against defunding police forces and did not support the Green New Deal.
3 PERSONAL INSULTS SIGNAL MORE UGLINESS AHEAD
At times, the debate descended into name-calling and insult-hurling. Mr Biden called Mr Trump a clown, a fool, a liar, and the worst president the US has ever had.
Mr Trump mocked Mr Biden's intellect, saying he graduated at the bottom of his class. "Don't ever use the word smart with me. There's nothing smart about you, Joe."
The debate got especially heated when Mr Trump went after Mr Biden's son Hunter, whom he accused without proof of corrupt business dealings. He also referenced Hunter's drug abuse and said he was "dishonourably discharged" from the military. Mr Biden, who had been in the middle of praising his late son Beau's military service in Iraq, said: "That is simply not true."
4 TRUMP DOUBLES DOWN ON ELECTORAL FRAUD CLAIMS
Asked about the integrity of the election, Mr Trump doubled down on his unsubstantiated claims of voter fraud, calling the election rigged and saying: "This is not going to end well."
He said he was urging his supporters to "go into the polls and watch very carefully", in contrast to Mr Biden's pledge to call on his supporters to remain calm on election night. Mr Biden also promised not to call a victory until the results had been independently certified.
Mr Trump's comments raise the chance of unrest should he lose.
5 MOST VOTERS HAVE ALREADY MADE UP THEIR MINDS
The debate is unlikely to close the gap between the candidates. Voting is already under way in many states and most people say their minds have already been made up.
Historically, polls also do not shift that much at this stage.
In a FiveThirtyEight analysis of polls from 1976 to 2012, the difference between polling leads just after the first debate and at the end of the campaign was an average of 2.2 per cent.
A Morning Consult poll released on Tuesday morning found that 86 per cent of voters say their position was immobile, with only 14 per cent saying they might change their mind.