Optimistic of US VP Kamala Harris's success in the swing state of Arizona, Barack Obama has once again endorsed the Democratic candidate, while grilling Donald Trump for not having enough stamina for taking up the president's office. 

In the city of Tucson, Obama and Harris came up with a new golden oldie punch at 78-year-old Trump, questioning his ability to serve a second term.

"Along with his intentions, there is also a question of his competence. Have you seen him lately?” asked Obama. “I mean, he is out there, he’s giving two, two-and-a-half hour speeches, just word salads. You have no idea what he’s talking about.”

"Tucson, we do not need to see what an older, loonier Donald Trump looks like with no guardrails," said Obama.

Democrats were quick to use age as a strike against Trump — now the oldest presidential candidate in US history — that was not long ago a worry, but recently became significant enough to make 81-year-old Joe Biden withdraw from his election bid.

Trump’s age factor has garnered attention due to several events where he appeared unsure of himself and various media cancellations, which Democrats highlight as proof of the Republican candidate's physical exhaustion from campaigning.

 “Tucson, we do not need to see what an older, loonier Donald Trump looks like with no guardrails,” said Obama.

“If he can’t handle the rigors of the campaign trail, is he fit to do the job?” Harris said at a rally in a must-win state of Michigan on Friday.

Harris and associates such as Obama with his wife Michelle are looking forward to mobilise voter support in must-win states that are crucial in deciding US presidential elections. 

Arizona, where Obama delivered a speech on Friday, is one of these swing states, with polling averages indicating that Trump has a slight lead of about two points.

Meanwhile in Michigan, where Harris spoke the same day, the Democratic Vice President is leading by less than one point.

Democrats have portrayed Trump as a dangerous and anti-democratic figure, claiming that his efforts are compensating for his loss in the 2020 election, in which he was defeated, and asserting that elections were not rigged against him either.