Kamala Harris and Donald Trump sparred on Tuesday in a contentious presidential debate that repeatedly went off the rails, as Trump pursued bizarre and often falsehood-ridden tangents about crowd sizes, immigration policy and abortion access.

The Philadelphia debate marked arguably the most significant opportunity for both Harris and Trump since Joe Biden withdrew from the presidential race in July, and the event began cordially enough. Harris crossed over to Trump’s podium to shake his hand and introduce herself, an acknowledgement that the two presidential nominees had never met face to face before Tuesday night.

But the cordiality did not last long. After delivering some boilerplate attack lines about the high inflation seen earlier in Biden’s presidency, Trump pivoted to mocking Harris as a “Marxist” and peddling baseless claims that Democrats want to “execute the baby” by allowing abortions in the ninth month of pregnancy.

That false claim was corrected by both Harris and the ABC News anchor Linsey Davis, who joined her fellow moderator David Muir in fact-checking some of Trump’s statements throughout the evening. Harris then segued into a stinging rebuke of Trump’s record on abortion, criticizing him for nominating three of the supreme court justices who ruled to overturn Roe v Wade in 2022.

“One does not have to abandon their faith or deeply held beliefs to agree the government and Donald Trump certainly should not be telling a woman what to do with her body,” Harris said. “And I pledge to you, when Congress passes a bill to put back in place the protections of Roe v Wade, as president of the United States, I will proudly sign it in to law.”

Despite broad public support for Roe v Wade, Trump boasted about his role in reversing it and applauded the supreme court’s “great courage” in issuing its ruling, while he dodged repeated questions about whether he would veto a national abortion ban as president.

Trump seemed to trip over himself even when moderators offered questions on his strongest issues, such as immigration. When asked about Biden’s handling of the US-Mexico border, Harris pivoted to discussing Trump’s campaign rallies.

“I’m going to invite you to attend one of Donald Trump’s rallies because it’s a really interesting thing to watch,” Harris said. “You will see during the course of his rallies, he talks about fictional characters like Hannibal Lecter. He will talk about [how] windmills cause cancer. And what you will also notice is that people start leaving his rallies early out of exhaustion and boredom. And I will tell you, the one thing you will not hear him talk about is you.”

The tangent appeared to be a blatant attempt by Harris to bait Trump into squabbling over attendance at his rallies instead of discussing immigration policy – and it worked. Trump began attacking Harris with baseless accusations that her campaign was paying people to attend her rallies while celebrating his own events as “the most incredible rallies in the history of politics”.

Then, rather than highlighting his immigration proposals, Trump chose to spread debunked claims that Haitian migrants in an Ohio city have started capturing and eating their neighbors’ pets.

“They’re eating the dogs. The people that came in, they’re eating the cats,” Trump said. “They’re eating the pets of the people that live there. And this is what’s happening in our country, and it’s a shame.”

The outburst instantly became a source of mockery on social media, as Democrats celebrated Trump for “doubling down on the crazy uncle vibe”, in the words of the transportation secretary, Pete Buttigieg.

Even as moments of the debate bordered on absurdity, other exchanges regarding foreign policy and the January 6 insurrection felt heavy with meaning. Pressed on his false claims regarding widespread fraud in the 2020 presidential election, Trump again refused to acknowledge his defeat, prompting a stark warning from Harris.

“Donald Trump was fired by 81 million people, so, let’s be clear about that. And, clearly, he is having a very difficult time processing that,” Harris said. “But we cannot afford to have a president of the United States who attempts, as he did in the past, to upend the will of the voters in a free and fair election.”

On foreign policy, Harris fielded difficult questions on the war in Gaza, as she expressed her support for Israel’s “right to defend itself” while calling for “security, self determination and the dignity they so rightly deserve” for Palestinians.

Asked about his own stance on the war, Trump reiterated his bombastic claims that his presence in the White House would have prevented the wars in both Gaza and Ukraine.

“If I were president, it would have never started,” Trump said. “If I were president, Russia would have never, ever. I know Putin very well. He would have never –and there was no threat of it either, by the way, for four years – have gone into Ukraine.”

And yet, when asked directly whether he wanted Ukraine to win its war against Russia, Trump deflected.

“I want the war to stop,” Trump said. “I think it’s the US’s best interest to get this war finished and just get it done, all right? Negotiate a deal because we have to stop all of these human lives from being destroyed.”

The debate ended with Harris vowing to be “a president for all Americans” while Trump attacked her as “the worst vice-president in the history of our country”. It was a fitting end for two candidates who offered starkly different visions for the nation in what might be their only presidential debate.

No other presidential debate has yet been officially scheduled, so the face-off on Tuesday may represent the last time that Harris and Trump meet before election day. The days ahead will determine whether the debate made a lasting impression on the undecided voters who will decide what appears to be a neck-and-neck race.

Read more about the 2024 US election: