WASHINGTON - US President Donald Trump and Democratic presidential nominee Joe Biden faced off on Tuesday (Sept 29) in the first presidential debate, just over a month from Election Day on Nov 3.

There will be two more debates between Mr Trump and Mr Biden and one between the vice-presidential nominees Mike Pence and Kamala Harris.

Here are five takeaways from the debate in Cleveland, Ohio.

1. EXTREME MESSINESS OF THE DEBATE

Tuesday night was less a debate and more a spectacle. Mr Trump, 74, did the lion's share of interruptions, frequently talking over Mr Biden, 77, and heckling him with short, sharp comments and questions.

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, adding: "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, while the President's detractors will call him a bully.

It remains to be seen whether Mr Trump's combative approach will endear him to undecided voters and white suburban women, whom he needs to win over to close in on Mr Biden's lead.

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.

Mr Biden also came under attack in the Democratic primaries but bounced back, suggesting that personal attacks do not work as well against him.

All in all, the barrage of interruptions meant that the two men could hardly engage with each other on substantive points, nor delve deep into policy discussions.

This meant that Mr Trump could skip quickly past uncomfortable moments and potential pitfalls. The debate breezed past his administration's handling of the pandemic, an area he has consistently received low scores in national polls for, and a bombshell New York Times report on his tax returns.

Mr Biden also could not effectively rebut Mr Trump when he made exaggerated claims, nor hold his feet to the fire for failing to condemn white supremacists or his lack of a comprehensive healthcare plan.

2. THE SPECTRE OF SOCIALISM

Mr Trump simultaneously 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 near the start of the debate, adding: "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, rendering Mr Trump's socialism line of attack less effective.

Over the course of the debate, Mr Biden explicitly said he was against defunding police forces and did not support the Green New Deal.

While neither are positions that will endear him to the left wing of the party, they will likely reassure skittish swing voters. They are also unlikely to irrevocably alienate left-wing Democrats, who are strongly opposed to Mr Trump and have been campaigning for Mr Biden.

3. PERSONAL INSULTS SIGNAL MORE UGLINESS AHEAD

The debate at times descended into name-calling and insult-hurling.

Mr Biden called Mr Trump a clown, a fool and a liar, told him to shut up, and called him the worst President the United States has ever had.

Mr Trump mocked Mr Biden's intellect, saying that he graduated the lowest in his class. "Don't ever use the word smart with me," said Mr Trump. "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 the younger Mr Biden'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."

"He's fixed it, he's worked on it," Mr Biden said of Hunter's drug problem. "I'm proud of him. I'm proud of my son."

4. TRUMP DOUBLES DOWN ON UNSUBSTANTIATED CLAIMS OF ELECTORAL FRAUD

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 that 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 victory until the results had been independently certified.

Mr Trump's comments raise the chance of unrest should he lose, with his supporters potentially unwilling to accept the election and its outcome as legitimate.

5. MOST PEOPLE HAVE ALREADY MADE UP THEIR MINDS

The debate was also unlikely to close the gap between Mr Trump and Mr Biden. Voting is already underway in many states, and most people say that their minds are made up.

Historically, polls also do not shift that much at this stage. According to 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 all voters say their position on the 2020 race was immobile, with only 14 per cent saying they might change their mind.

Party voters were similarly set in their ways, with 9 per cent of Democrats and 11 per cent of Republicans saying they were open to change. Just over a quarter of independents say they might change their mind.