Joe Biden and Donald Trump clashed on their respective records as they went head to head in the first ever debate between a current and former U.S. president in Atlanta, Georgia, on Thursday evening.

In a 90-minute debate without an audience and featuring few direct exchanges, Biden started hesitantly and Trump answered steadily in a halting clash that featured repeated accusations of lying and claims the other was "the worst president in U.S. history."

A CNN flash poll of debate watchers suggested an overwhelming 67 percent to 33 percent victory for Trump, the Republican, on the night, a potentially key event in an election which polls indicate is again likely to be decided by a small number of voters in a handful of battleground states.

The debate, held almost four months before the November 5 election, covered issues with top voters' concerns, including the cost of living, immigration, abortion rights and democracy, and touched on the Ukraine and Gaza crises, though little light was shed on the candidates' policy agenda.

Biden's age concerns

Biden went into the debate needing to reassure voters that his age was not a barrier to him serving a second term as president. He would be 86 at the end of the second term, in four and a half years.

He started hesitantly and sounded slightly hoarse, but slowly grew more fluent as he responded angrily to Trump's answers on abortion and veterans, and answered more confidently on questions related to the January 6 riots and Trump's legal problems.

However, in an election in which the candidates' age and capacity to do the job is one of the foremost issues, the reaction of senior Democrats to the president's performance was one of concern.

In previous set pieces events, such as the State of the Union, Biden had risen to the occasion, but it was difficult for his surrogates to make that argument on Thursday.

"It was a really disappointing debate performance from Joe Biden. I don't think there's any other way to slice it," Kate Bedingfield, the president's former communications director, said on CNN. "His biggest issue that he had to prove to the American people was that he had the energy and the stamina, and he didn't do that."

Trump sought to criticize the clarity of Biden's answers. "I really don't know what he said on this, and I don't think he knows what he said either," he said after a question on immigration. A lack of precision from Biden also opened the door for Trump to take charge of the narrative and pivot away from his own vulnerabilities.

And while Biden did hit some key points that matter to undecided voters, including Trump's legal challenges and the January 6 riots, a difficult start was compounded by a poor closing, causing concern about a low-energy performance and its consequences both for the candidate and down-ballot Democrats.

Trump sticks to a script

Whereas in the 2020 debates Trump was aggressive and consistently interrupted Biden, on Thursday he took a more measured approach.

He avoided answering direct questions, sometimes completely, and his statements were regularly fact-checked by the media as being false (though not by the debate moderators). However, his presentation was coherent and he answered in a moderate, if characteristically confident, style, even managing to say "let's not act like children" when the men started arguing over golf.

The debate rules, which prevented interruptions by muting a candidate when it wasn't his time to speak, may have helped Trump. His son, Don Jr, wrote on social media that the rules had kept the former president "disciplined and focused."

On policy, his only notable shift away from the right of his party was on abortion. He said he would support access to the abortion pill mifepristone, an attempt to address one of his weakest points with the electorate, his championing of restrictions to abortion rights. 

Trump's approach to abortion rights is a major attack line for the Democrats since the overturning of Roe v. Wade, which had enshrined the right to an abortion in federal law.

'Failing' vs 'greatest'

Though the debate didn't shed much light on policy specifics, the exchanges did make clear the men's starkly different visions and understanding of their country.

Trump was relentlessly positive about his own time in the White House and dismissive of Biden's, whereas Biden tried to make the case for his achievements in office and hit out at Trump's record.

Trump repeatedly said the U.S. is a "failing nation" that isn't respected around the world, and accused Biden of "driving the world toward World War Three" and "destroying our country."

Biden insisted the U.S. was "the most admired country in the world" and said, "we have the finest military in the history of the world, the finest in the history of the world. No one thinks we're weak. No one wants to screw around with us, nobody."

Biden argued that Trump left him an economy in shambles, while Trump said the economy was the "greatest in the world" before the arrival of COVID-19.

Trump defended his tax cuts, saying they spurred economic growth, while Biden said Trump just wanted to give more tax cuts to the rich. Trump accused Biden of "causing inflation," Biden retorted that Trump mishandled the pandemic and that led to higher inflation.

The debate got personal when the moderators turned to Trump's legal troubles. Biden accused Trump of having "the morals of an alley cat," and Trump said Biden was the worst president in U.S. history, a claim Biden later turned back on Trump.

Trump blames Biden for Gaza, Ukraine crises

Questions on foreign policy were limited, but both the Ukraine and Gaza crises were addressed, as was the United States' role in the world.

Trump claimed both crises came about as a result of "weakness" under Biden, and insisted neither would have happened had he still been president. He also said Biden should be demanding that NATO members in Europe contribute more to defense.

On Gaza, Biden said all major players had endorsed the three-stage plan for Gaza he put forward, including Prime Minister Benjamin Netanyahu, other than Hamas. He tried to walk a line between support for Israel and urging restraint, while Trump said Israel should be allowed to "finish the job."

Trump also called Biden's withdrawal of troops from Afghanistan "the most embarrassing day in the history of our country's life."