Donald Trump constantly attacked his Democratic opponent Joe Biden over his age and fitness, but the 78-year-old Republican could find those same arguments coming back to haunt him after the president ended his reelection bid.
With Vice President Kamala Harris, 59, on course to become the Democratic nominee, Trump will be a much older candidate and face an even brighter spotlight on any hint of decline.
"The dynamics have drastically changed," Matthew Foster, a political scientist at American University, told AFP.
Trump continued to attack Biden's mental acuity even after he dropped out, taunting on social media that he is "going to wake up and forget that he dropped out of the race."
The barbs are almost enough to make one forget the real estate mogul is not all that young either.
If Trump wins the November election, he will be the oldest American president to be sworn in.
But the Republican nominee is fallible, with his own repeated gaffes and strings of disjointed tirades.
The question of whether they illustrate his own cognitive decline or are simply one-offs is hard to say.
His hour-and-a-half long nomination acceptance speech at the Republican National Convention in Milwaukee -- just five days after surviving an assassination attempt -- has been touted by his supporters as an illustration of his endurance.
Some viewers, however, watched the speech and saw a candidate who was much more tired than usual, sweating through a weak speech delivery.
According to an ABC poll conducted in mid-July, 60 percent of Americans said Trump was too old to run for a second term.
As soon as Biden withdrew from the race, Trump's age also came under fire -- but he has consistently dismissed the concerns.
In January, he told supporters that he had completed a cognitive test given by his doctor and he "aced" the results.
"I'll let you know when I go bad; I really think I'll be able to tell you," Trump said at the time.
However, the former president is not subject to the same demands of medical transparency as he was when he was in the White House.
Over the past few years, little information about Trump's health has come out.
Last November, the former reality television host simply published a brief letter from his doctor stating he was in good health and that he had lost weight -- without specifying how much.
Harris's campaign team became fully operational Sunday, and though it is still fine-tuning its strategy, there is little doubt Trump's age will be one of the 59-year-old candidate's lines of attack.
Harris campaign spokesman James Singer said in a statement to AFP "the Republican party has nominated Donald Trump, a 78-year-old convicted criminal who has spent decades screwing over working people."
Foster said Harris "brings an absolutely different kind of energy" to her campaign, describing her style as "younger" and "aggressive."
Harris, a former senator from California whose first presidential campaign in 2020 fizzled out, made her mark by standing out during the televised debates.
At the time, Harris and Biden were up against one another; now she has been called by him to carry the torch.
