Former US President Donald Trump, 78, hurled hyperbole at President Joe Biden, 81, who seemed to lose his train of thought during the debate at the CNN headquarters in Atlanta.

The two oldest presidential hopefuls in US history clashed over immigration, abortion and even golf.

Here are six key takeaways from the first US presidential debate:

Biden put on a muted performance

Biden, who already faces criticism over his age was unable to match the energy of Trump, who is only three years his junior.

The incumbent president resorted to raspy rambling and appeared to struggle with articulating his words. At one point, he referred to “billionaires” as “trillionaires” before going back to correct himself.

Biden made some robust criticism of Trump’s leadership during COVID-19 and its impact on the economy, and mocked some of Trump’s responses to COVID-19 safeguards at the time. “Just inject a little bleach into your arm, and you’ll be alright,” he said.

However, his tone fell flat against his more bombastic opponent, especially during the early stages of the debate. Later on, Biden somewhat picked up the pace to push back against Trump’s slew of factually incorrect assertions about immigration and abortion.

However, Democrats raised the alarm over Biden’s performance, with some even starting to talk about replacing him on the presidential ticket.

“There are going to be discussions about whether he [Biden] should continue,” David Axelrod, former senior adviser to former President Barack Obama, told CNN.

While Biden’s Vice President Kamala Harris backed him after the debate, saying substance matters over style in this election, even she conceded “it was a slow start”.

Presidential hopefuls came to blows over golf

Biden and Trump went back and forth over which of them is physically and cognitively stronger.

Trump boasted about his strength, claiming, “I’m in as good shape as I was 25, 30 years ago,” to moderators Jake Tapper and Dana Bash.

In response, a snickering Biden implied his opponent was lying about both his height and weight.

Trump said he had won two championships on his golf course while Biden “can’t hit the ball 50 yards”.

This prompted Biden to challenge Trump to a golf match, only if Trump would carry his own bag.

“Let’s not act like children,” said Trump.

“You are a child,” responded Biden.

Trump called Biden a ‘bad Palestinian’

“We are the biggest producer of support for Israel of anyone in the world,” Biden said, reiterating US support for Israel’s war on Gaza in which more than 37,718 Palestinians have been killed since October last year.

Biden added that his administration is continuing to send experts and intelligence to hinder Palestinian group Hamas in the war.

Trump snapped back, saying it is Israel that wants to continue with the war, “and you should let them go, and let them finish the job. He [Biden] doesn’t want to do it. He’s become like a Palestinian, but they don’t like him because he’s a very bad Palestinian, he’s a weak one”.

In the nearly nine months of the war that has left Gaza rife with power outages and food insecurity, the United States has provided military and diplomatic assistance to Israel, and has repeatedly blocked ceasefire resolutions. A US-sponsored resolution endorsing a ceasefire proposal eventually only passed at the United Nations Security Council (UNSC) some eight months into the war.

Biden accused Trump of lying about abortion

Trump invoked anti-abortion sentiment by accusing Biden and his party of allowing late-term abortions.

During the debate, Trump claimed Biden and Democrats would be “willing to, as we say, rip the baby out of the womb in the ninth month”.

“You’re lying. That is simply not true,” Biden refuted Trump’s assertion. “We are not for late-term abortion, period. Period.”

Trump also said of Democrats: “They will take the life of a child … even after birth”, despite the fact that infanticide is illegal in every US state.

In the US, late-term abortions are uncommon and are usually a last resort when there are serious complications with a wanted pregnancy.

According to the Centers for Disease Control and Prevention, fewer than 1 percent of abortions were performed at or after 21 weeks in 2020.

Immigration dogged the debate

Throughout the debate, Trump turned the topic to immigration, accusing Biden of “opening up the safest border in the world to terrorists, prisoners”.

He accused Biden of being “the one that killed people with a bad border and flooding hundreds of thousands of people dying and also killing our citizens when they come in”.

Biden on the other hand recounted the work his administration has done to manage an influx of illegal immigrants, including tightening border security and working on the bipartisan National Security Agreement.

“By the way, the border patrol have endorsed me, endorsed my position,” a wide-eyed Biden said. “When he [Trump] was president, he was separating babies from their mothers, putting them in cages, making sure their families were separated. That’s not the right way to go”.

Trump snapped back, saying, “the border patrol, I won’t say that, but they endorsed me for president”.

Trump refused to say if he would honour election result

Trump did not directly answer whether he would honour the result of the election.

He said he would only accept the results if the election is “free and fair”, reiterating false claims that the 2020 presidential election, which he lost to Biden, was rigged against him.

“The fraud and everything else was ridiculous,” he said.

Following the 2020 election result, Trump incited his supporters to storm the US Capitol in the infamous January 6, 2021 Capitol riots.

During the debate, Trump downplayed the riots, which were the deadliest attack on US power in more than 200 years. “They talk about a relatively small number of people that went to the Capitol and in many cases were ushered in by the police,” he said.

The next presidential debate is slated for September 10 and will be hosted by ABC news.