Donald Trump, 78, challenges Joe Biden, 81, to a cognitive test but then fluffs the name of his doctor and forgets to take questions before walking off stage at end of speech

It was meant to be a chance to underline the differences between a vigorous 78-year-old Republican candidate and the frail 81-year-old incumbent. 

But Donald Trump apparently suffered two embarrassing memory lapses on Saturday evening even as he challenged Joe Biden to a cognitive test.

Not only did he misremember the name of his doctor during his speech to supporters but he also seemed to forget a promise to answer questions at the end of the appearance and simply walked off stage when he was done.

In so doing he reminded voters that the choice this November is between the two oldest presidential candidates in history. 

'At the end of the speech, I'll be taking some questions,' he said at the start of his speech to 8000 adoring fans at a convention center in Detroit, Michigan. 

'So this is different than Joe Biden. He doesn't take any questions.'

Former President Donald Trump spent Saturday in the key swing state of Michigan, where he addressed Turning Point Action's People's Convention in the evening

He went on to speak for about an hour and 20 minutes (far more than Biden's usual 15 minutes) in his usual freewheeling style. But at the end he appeared to have forgotten his promise. 

With the audience cheering and the clear absence of his usual walk-off music, Trump stood on stage for several seconds thanking his supporters. 

Only then did 'Hold On, I'm Comin,' the song by Sam and Dave, kick in.

An anxious looking Charlie Kirk, founder of Turning Point Action which organized the gathering of conservatives, hurried  on stage to confer with the former president, who was already heading into the wings.

'One more time ... give it up for President Donald Trump,' he said, bringing the evening to its conclusion.

It was an odd ending to a typically rambunctious speech. He laid out his priorities if he wins the presidential election and repeatedly slammed his Democratic opponent.

But on the day after his 78th birthday, he showed signs of frailty. 

'He doesn't even know what the word inflation means,' he said of Biden. 'I don't think if you gave him a quiz. .. I think he should take a cognitive test like I did. 

'I took a cognitive test. And I asked him, Doc Ronnie, Doc Ronnie Johnson. Does everyone know Ronnie Johnson congressman from Texas, he was the White House doctor?

Trump spoke for about an hour and 20 minutes in his usual freewheeling style

The convention center was filled by 8000 attendees on Saturday evening

Trump received a rapturous reception from supporters, as fireworks lit up the room

 Except he wasn't. Trump's White House physician and the congressman from Texas is called Ronnie Jackson.

Trump is ahead of Biden in the polls, and has made much of his vigorous approach to campaigning compared with the Democrat's fragility.

But he also makes frequent verbal slips and a recent report suggested that his rambling speech worried some chief executives during a meeting.

He spent Saturday in Detroit, Michigan, taking on his rival in what should be a reliably Democratic city.

In the evening he addressed 8000 supporters at Turning Point Action's People's Convention. 

A supporter of former President Donald Trump wears an "Adorable Deplorable" shirt, a reference to Hillary Clinton's comment about Trump supporters, at Turning Point Action's "The People's Convention" on June 15, 2024 in Detroit

He slammed the Bidens for shuttling back and forth across the Atlantic aboard Air Force One, making multiple trips to Europe and, in the case of the first lady, returning to the U.S. for barely 24 hours to support Hunter at his trial.

And he promised to begin to unravel Biden's policies on day one of taking office.

'By this time next year, America’s borders will be shut, sealed, and secure ...' he said. 'Inflation will be in full retreat. 

'Our economy will be roaring back. Optimism will be surging. American pride will be soaring. 

'The American Dream will be thriving again for citizens of every race, religion, color, and creed.'

About 1000 people gathered at the 180 Church in Detroit, Michigan to hear Trump speak

Guests listen to the national anthem prior to the start of a roundtable with Republican presidential candidate and former President Donald Trump at the 180 Church

The speech also included the usual grab bag of grievances and wild claims: That the Army is building electric tanks, that President Volodomyr Zelensky is the greatest salesman in history, that dishwashers are being deprived of water, and that the 2020 election was stolen.

Trump's itinerary highlighted the tightrope he is trying to walk in the 2024 election, first visiting an African-American church before speaking at a Turning Point Action gathering, a group which the Anti Defamation League says attracts racists and extremists. 

Biden won Michigan in 2020 by three points. But now the former president has inched ahead with a half-point advantage in rolling poll averages. 

'We think we're going to win this state. We're leading right now by a lot,' Trump said earlier during a roundtable at 180 Church in the north-west of the city.

'So it's an honour to be here. It's a very important area for us.'

The schedule shows how the political landscape is changing in 2024, as Trump tries to court the Black vote that did so much to land Biden the White House. 

'He's been the worst president for Black people,' said Trump.