PHILADELPHIA: The United States presidential elections on Tuesday witnessed a key development as former US president and Republican nominee Donald Trump went toe-to-toe with incumbent Vice President and Democratic candidate Kamala Harris in their first televised presidential debate.

The presidential debate saw both Trump and Harris battling it out over immigration, abortion, diplomacy and other key issues and was a more energised showdown than the one two months ago in Atlanta, where President Joe Biden's disastrous debate performance led to his withdrawal from the race, and the ascension of Harris.

Here are five takeaways from Tuesday's presidential debate.

Combative demeanour

The ABC News debate rules were meant to maintain decorum, but the candidates sparred, sometimes interrupting one another — and with a clearly prepared Harris baiting her rival on multiple issues.

Harris attacked Trump on his record, his bombastic style, and the "bunch of lies" he routinely dishes out. Using pointed language, Harris said she and Biden worked to "clean up Donald Trump's mess."

She accused Trump of having "a very difficult time processing" his 2020 election loss and, in comments that clearly infuriated the billionaire Republican, mocked him for how some supporters leave his rallies early.

Trump pushed back — "Wait a minute, I'm talking now," he said at one point when Harris interjected — and launched lengthy tirades about the Biden administration's "insane" immigration and economic policies.

Trump often looked down, and rarely at Harris when she spoke. The vice president routinely turned to her rival, either to deliver a critique or raise her eyebrows at a Trump remark.

Abortion issue

Their early clash was over reproductive rights. With the Supreme Court, empowered by three Trump-nominated justices, overturning federal abortion protections, Trump has sought to moderate his position on abortion.

He argued he succeeded in returning the issue back to the US and said:

"It's the vote of the people now. It's not tied up in the federal government."

"I did a great service in doing it, it took courage to do it," the former president added.

Trump also repeated a false claim that some states allow abortions "probably after birth," a procedure illegal nationwide.

"This is what people wanted? Pregnant women, who want to carry a pregnancy to term, suffering from a miscarriage, being denied care in an emergency room because the health care providers are afraid they might go to jail and she´s bleeding out in a car in the parking lot?" Harris countered, pointing at Trump while he stared ahead, stone-faced.

Immigration conspiracy

Trump's parroting of a debunked theory about immigrants eating Americans' pets was perhaps the apex of his falsehoods, along with his repeated claims that the 2020 election was stolen from him.

He dived into the unfounded conspiracy that Haitian immigrants in a small Ohio city were stealing pets for food.

"In Springfield, they're eating the dogs [....] They're eating the cats, they're eating the pets of the people that live there," Trump seethed.

When called out by ABC moderators who said city officials have found no credible evidence of such crimes, Trump bizarrely claimed "people on television" said it.

Diplomacy duel

Foreign policy largely took a back seat, although each candidate took the opportunity to hammer the other on diplomacy and offer radically different visions of the world.

Harris called Trump "weak and wrong" on national security, and got under his skin when she said he was the laughingstock of world leaders.

She warned Trump would "give up" Ukraine to Russian President Vladimir Putin, "a dictator who would eat you for lunch."

Trump by contrast branded her a "horrible negotiator" who "hates Israel."

"If she's president, I believe that Israel will not exist within two years from now."

Revenge for Biden

Some feared Harris would flounder under Trump´s attacks. But the Democrat, clearly well-prepared, laid out her own arguments while putting her rival on the defensive, according to analysts.

"Trump was terrible and Harris won hands down," University of Virginia professor of politics Larry Sabato told AFP. "She got revenge for Biden's loss in the first debate."

"The VP executed her strategy to a tee, parrying the moderator's questions, landing jabs at Trump, and baiting him into angry lunges," added Republican strategist Liam Donovan.

Princeton University professor Julian Zelizer, described it as Harris's "precision and plans versus chaos, rage and disinformation" of Trump.