Before Thursday evening, many Americans had expressed concerns about Joe Biden’s age and fitness for office. To say that this debate did not put those concerns to rest may be one of the greatest understatements of the year.

The president came into the debate with a low bar to clear, and he stumbled. He was flat. He was rambling. He was unclear.

Roughly midway through the debate, the Biden campaign told reporters that the president was been battling a cold - an attempt to explain his raspy voice. That may be so, but it also sounded like an excuse.

For 90 minutes, more often than not, Joe Biden was on the ropes. Particularly early in the evening, some of his answers were nonsensical. He ended one answer by saying, “We finally beat Medicare” – an odd reference to the government run healthcare programme for the elderly.

Mr Biden's own former communications' director Kate Beddingfield was on CNN immediately after the debate, and she was clear: "There's no two ways about it, that was not a good debate for Joe Biden."

She said his mission was to prove he had the energy and the stamina, and he failed.

As the debate progressed, like a boxer on the ropes, Biden started to take big swings against his opponent in an attempt to change the momentum. A few of those swings may have landed, provoking the former president into angry responses

That the first few topics were on the top voter issues of economy and immigration - which polls show Americans trust Donald Trump more on - only made the problem worse for the president.

“I really don’t know what he said at the end of that sentence, and I don’t think he did, either,” Trump quipped after another Biden response. That line may have summed up the night.

A more focused Trump

The former president largely offered a disciplined, nimble performance. He avoided the kind of interruptions and belligerence that undermined his first debate showing in 2020 and turned the discussion back to attacks on Biden’s record whenever possible.

He repeatedly made assertions that weren't supported by facts as well as outright falsehoods, but Biden largely was unable to corner him on them.

When the topic turned to abortion, for instance, the former president repeatedly shifted attention to what he said was Democratic extremism. He claimed, incorrectly, that Democrats support abortions after babies are born.

Abortion is an issue that has proven to be a weakness for Trump and Republicans in general since the overturning of Roe v Wade - which had protected the constitutional right to abortion - by the Supreme Court in 2022. But Biden’s attacks in an area where he could have scored points fell flat.

“It’s been a terrible thing, what you’ve done,” Mr Biden said.

A fighter on the ropes

At times during this debate, President Biden effectively swung back, provoking former president Trump into angry responses.

In a memorable line, Mr Biden, noting Trump’s conviction on charges that stemmed from an alleged romantic liaison with adult film star Stormy Daniels, said the former president had “the morals of an alley cat”.

“I didn’t have sex with a porn star,” Trump snapped back.

Trump also appeared on the back foot when talking about his response to the 6 January attack on the US Capitol. He initially tried to turn a question about his responsibility for the Capitol riot into a condemnation of Biden’s record, but this time the president wouldn’t let him off the hook.

“He encouraged those folks to go up to Capitol Hill. He sat there for three hours as his aides begged him to do something,” Mr Biden said. “He didn’t do a damn thing.”

What happens next?

This is the earliest debate in modern US history, in part because the Biden team wanted it that way. One reason is they wanted to shift focus to Trump earlier in the campaign season, hoping that American voters would be reminded of the chaotic nature of his presidency.

But more people will be talking about Mr Biden’s performance after this debate than the former president’s.

Another reason the Biden team may have wanted an early debate is that it would give their candidate more time to recover from a weak performance. In the end, this may be what gives them comfort after Thursday night.

The Democrats have their convention in August, when they will be able to offer a more scripted vision of a second Biden term for Americans. And there’s another debate scheduled for September, which - if it happens - will be fresher in American minds as they head to the polls in November.

That may be cold comfort for Democrats, though, as they may be wondering whether a second chance at Mr Trump on the debate stage will turn out any different for their man. And some, at this point, may be thinking about how they might get a different nominee at their August convention.