It took only minutes for the video of President Trump’s slow and halting descent down a ramp at the U.S. Military Academy at West Point to begin circulating online on Saturday, accompanied by a blunt hashtag that now doubles as a campaign slogan for his opponents: #TrumpIsNotWell.

The viral clip, which has since been repackaged into Twitter barbs and a political attack ad directly challenging Trump’s vigor and vitality, highlighted how questions over physical and mental health have become a leading attack line in the 2020 presidential race.

For Trump, who has tried to cast his Democratic rival, Joe Biden, as “sleepy” and mentally absent, the attacks over his own wellness appeared to hit close to home. The president defended himself by offering a credulity-straining explanation for his unsteady gait, describing the standard-looking ramp as “steep” and “very slippery.”

In the first presidential race in which the combined age of the two leading candidates exceeds 150 years, mental acuity and physical health have become a central theme as the 77-year-old Biden and the 74-year-old Trump compete for votes. While previous presidential contests have included whisper campaigns and rumors about candidates’ health, the open charges of senility flying between the two camps sets the 2020 contest apart, said Barbara Perry, a presidential historian at the University of Virginia’s Miller Center.

“These kinds of rumblings used to happen behind the scenes,” she said. “And now, because of both social media and the attack style of campaigning that Trump uses, there’s been this turning point.”

The Trump campaign’s eagerness to focus on Biden’s verbal gaffes could be a “double-edged” sword as attention turns back to the president’s own behavior, she said.

Neither campaign nor their allies have provided anything to back up the attacks on the two men’s health beyond their observations on Trump and Biden’s public comments and physical appearance at times. Physicians for both Biden and Trump have released letters declaring the two men healthy.

As the video of Trump on the ramp trended online Saturday, the president took to Twitter to explain his cautious stroll.

“The ramp that I descended after my West Point Commencement speech was very long & steep, had no handrail and, most importantly, was very slippery,” Trump wrote. “The last thing I was going to do is ‘fall’ for the Fake News to have fun with. Final ten feet I ran down to level ground. Momentum!”

But the explanation was belied by the video — which showed the president pursing his lips while looking down as he gingerly made his way down the ramp. Trump only slightly increased his gait to a more normal speed for the final two steps of the journey. The general at his side seemed to have no trouble walking down the ramp.

Trump has regularly attacked Biden over his mental fitness for office, accusing his fellow septuagenarian of losing “his fastball” and having to rely on staff to function.

“I honestly don’t think he knows what office he’s running for,” Trump said during a campaign rally in March, telling supporters that Biden would only be a figurehead if he became president. “They’re going to put him in a home and other people are going to be running the country and they’re going to be super left radical crazies.”

As Biden has mostly stayed at his home in Delaware in recent months due to the coronavirus pandemic, the president and his campaign have sought to depict him as doddering in his basement and ill-equipped to lead the country through challenging times.

“Any honest voter juxtaposing President Trump and the democrat candidate can see the stark difference in mental acuity and wit,” said Ken Farnaso, a spokesman for the Trump campaign. “It isn’t their age that is in question here, it’s their track record and ability to go head-to-head with foreign leaders, friend or foe.”

But the campaign and some of the president’s allies have at times explicitly made Biden’s age an issue. In March, the Trump campaign ran ads on Facebook depicting Biden as a spoon-fed invalid in a nursing home, with the caption “Too Old?”

Some Trump advisers have said Biden’s age and long record in Washington will allow Trump to again run as an insurgent outsider, recapturing the energy and enthusiasm that helped him win in 2016.

Last week, Trump campaign manager Brad Parscale released a statement calling on the news media to air all of Biden’s public remarks.

It’s not clear if the strategy is working, as polls continue to show Biden leading Trump nationally and in key swing states. Biden’s significant lead among older voters, a group Trump carried in 2016, offer an indication that the president’s attacks alluding to his 77-year-old rival’s age could be backfiring.

John Anzalone, Biden’s pollster, has said the former vice president’s long track record and familiarity with older voters has boosted his standing, even as Trump has tried to brand him as senile.

“We’d be happy to be dead even with seniors. Or even lose them by a couple points because it would be a total game changer,” said Anzalone, who noted that Trump won seniors by seven percentage points according to 2016 exit polls and Mitt Romney won them by 12 percentage points in 2012.

He highlighted states such as Michigan, Wisconsin, Pennsylvania and Florida as home to large numbers of seniors.

Given Biden’s relatively moderate record on many issues, he is “not scary” to a lot of seniors, Anzalone said. He added that Trump’s erratic response to the coronavirus pandemic has weakened his position with voters over 65, who are more vulnerable to the contagion.

Trump, who has held several events at the White House in recent weeks catering to senior citizens, participated in a roundtable on Monday to tout his administration’s record.

“We have to keep all of our seniors safe, this is a very perilous time,” Trump said.

A Washington Post-ABC News poll released May 31 found Biden leading Trump among older registered voters by 10 points, 54 percent to 44 percent. The poll also found that only 46 percent of voters thought Trump had the “mental sharpness” necessary to serve effectively as president. For Biden, the number was 51 percent.

In a statement, Biden campaign spokesman Andrew Bates said the nation was “crying out for leadership” while Trump is “trampling on our highest values.”

“But instead of finally doing his job, Donald Trump — who weeks ago encouraged drinking disinfectant on national TV — somehow decides it’s a good idea to again raise the subject of mental acuity,” Bates said, referring to an instance in which Trump publicly mused about the effectiveness of injecting disinfectant to treat coronavirus patients.

Trump’s opponents, who have long attacked his mental sharpness, are now seizing on his physical fitness as well. In addition to the video of Trump struggling to walk down the ramp, another viral clip circulated Saturday in which Trump had to use a second hand to lift a glass of water to his mouth.

As outside groups began crafting campaign ads featuring the videos, Republican operatives working on the Lincoln Project — an anti-Trump group whose ads have provoked the president’s ire — amplified the hashtag #TrumpIsNotWell over the weekend.

For his part, Biden has avoided directly challenging Trump over his age — though he has sharply criticized the president for his handling of the pandemic and seized on some of Trump’s questionable claims to cast doubt about his fitness to lead.

Perry said Biden is following a more traditional political playbook, avoiding making untoward direct attacks on an opponent’s age, health or appearance — allowing outside actors to bring such issues into the public debate.

“He is old school and that’s one reason that that would not come naturally to him,” she said. “But you do have to be careful not to bring a knife to the gunfight, if your opponent is not following the old gentlemen’s agreement and the old rules.”

Some Biden supporters have pushed him to take Trump on more directly and more aggressively on the issue of mental and physical fitness. Some have highlighted how Trump effectively raised doubts about Hillary Clinton’s health in 2016.

Philippe Reines, a former top Clinton adviser who prepped her for the debates with Trump, publicly pleaded with Biden to take Trump on over his health.

“PLEASE force the TRUTH about donald trump’s physical & cognitive health into the open,” he wrote on Twitter on Saturday. “BEFORE his LIES about YOUR health harden any further.”

While the Biden campaign avoided directly criticizing Trump on his foibles over the weekend out of what campaign officials describe as a desire to take the high road and avoid cheap shots at the president — Biden’s allies had no hesitation poking at Trump.

“Trump can talk the talk, but literally — literally cannot walk the walk,” said South Carolina state Sen. Dick Harpootlian, a longtime Biden pal.

“He’s been so vociferous in his attacks on Joe Biden — calling him Sleepy Joe — and here’s a guy who, who obviously had trouble holding a glass of water walking down a ramp,” he added, joining a growing call for Trump to release his full medical records.

“There’s something here,” Harpootlian said. “How many metaphors can I use? Where there’s smoke there’s fire.”