Hollywood loves a sequel, so it is fitting that the current US presidential contest is a repeat of the bitter 2020 slugfest.

The recent presidential debate between Joe Biden, the incumbent 81-year-old Democrat, and Donald Trump, his 78-year-old Republican challenger, has been widely portrayed as a contest between a geriatric octogenarian drifting gently into senility, and a hate-spewing lunatic recently convicted for using campaign funds to pay a porn star hush money.

How has it come to this in the world’s richest country, with its dynamic innovators and elite universities?

Though fewer than half of Americans view either candidate favourably, much of the US “liberal” corporate media focused on Biden’s apparently disastrous debate performance, with the New York Times and CNN’s talking-heads calling for his resignation. Several senior Democrats continue to voice discontent.

In stark contrast, conservative media and Republican politicians have doggedly defended Trump, showing the ruthless discipline that has enabled them to reverse decades of progressive legislation.

Astonishingly, centre-left critics were surprised by Biden’s lack of mental acuity during the debate. Yet just this year he has verbally mistaken former German chancellor Angela Merkel for the dead former chancellor Helmut Kohl; erroneously referred to French President Emmanuel Macron as the dead Gallic president Francois Mitterand; and mistakenly described Egypt’s leader as the “president of Mexico”. In 2023, Biden stated that Russia was losing the “war in Iraq” and noted that “over 100 Americans” had died of Covid-19 (the actual figure is 1.2-million).

In 2022, Biden called out onstage to Republican congresswoman Jackie Walorski before being reminded that the legislator had died a month earlier. Critics of his debate performance also appear to have ignored the recent description of Biden by special counsel Robert Hur — who cleared the president of charges of mishandling classified documents — as “a sympathetic, well-meaning elderly man with a poor memory”.

Trump has similarly experienced his own “senior citizen moments”. He verbally confused Biden with former president Barack Obama seven times, while also mistakenly referring to his Republican rival, Nikki Haley, as former Democratic House speaker Nancy Pelosi.

The contestants pointedly did not shake hands before or after this presidential debate, underlining the lack of civility that now pervades US politics. Biden was widely portrayed as hoarse and halting, while Trump was depicted as fierce and forceful. The president sought to paint his opponent as a danger to democracy, architect of the Supreme Court decision to deny women the right to abortions, and a climate change denier. He wrongly claimed to have inherited 9% inflation from Trump instead of 1.4%.

Trump was characteristically full of bombast and bluster, lying brazenly throughout the debate. He falsely accused Biden of letting criminal illegal migrants into the country, erroneously claiming these migrants are stealing jobs from blacks and Hispanics.

He xenophobically described Biden as a China-funded “Manchurian candidate” and a “bad Palestinian” who had failed to fully back Israel’s military assault on Gaza. Trump further alleged that Biden had “encouraged” Russia to attack Ukraine, strangely accused Democrats of backing abortions after babies had been born, downplayed the attack on the Capitol by his supporters in 2021, and refused to say unequivocally whether he would accept the result of November’s election.

Given Biden’s frequent memory lapses before this debate the panicked reaction of his supporters to his lacklustre performance is somewhat disingenuous. I watched the full debate having factored in Biden’s weaknesses, and felt he actually remembered many facts and landed some good punches.

Trump certainly did not win this debate on substance, and if the ability to appear mentally fitter than your opponent while spewing bile and being economical with the truth is enough to triumph, this is a rather low bar for a country that likes to pride itself on being the “greatest nation on earth”.

• Adebajo is professor and senior research fellow at the University of Pretoria’s Centre for the Advancement of Scholarship.