LONDON — President Trump got a well-wishing phone call this past week from one of the few foreign leaders who knows what he’s been going through: Prime Minister Boris Johnson of Britain, the survivor of a serious brush with the coronavirus this spring.
Mr. Trump seized on the call as another opportunity to boast of a swift recovery from Covid-19. But he should take little comfort from Mr. Johnson’s experience — and not just because the prime minister ended up in an intensive-care unit after he, like the president, tried to work through the illness.
Six months after Mr. Johnson was released from the hospital, he has yet to shake off questions about the effects of the disease on his energy, focus and spirit. His health is a source of whispered speculation in the hallways of Parliament, questions from reporters and ominous musings by columnists, for whom Mr. Johnson’s illness has become a symptom of his broader political decline.
“It’s a metaphor for his government, and that’s affecting him personally,” said Jonathan Powell, who was chief of staff to Tony Blair when he was prime minister. “He looks like the wrong man for the job at this time.”
Parallels between Mr. Johnson and Mr. Trump are often overblown, and there is little in the prime minister’s convalescence that compares to the daily spectacle of a president pronouncing himself back to normal and scheduling campaign rallies a week after being airlifted to the hospital with trouble breathing.
Still, the two men share a penchant for brash statements, flouting the rules and a campaign-style approach to government. Both also initially played down the threat of the virus — Mr. Johnson, most notoriously, when he bragged about shaking the hands of coronavirus patients while visiting them in the hospital.
Despite his efforts, Mr. Johnson has never recaptured the public buoyancy that propelled him to a landslide election victory last December. On Tuesday, speaking to his Conservative Party’s annual conference, he tried again to put to rest questions about lingering effects of Covid-19, the disease caused by the virus.
“I have read a lot of nonsense recently about how my own bout of Covid has somehow robbed me of my mojo,” the prime minister said in a tone of theatrical umbrage. “And of course, this is self-evident drivel, the kind of seditious propaganda that you would expect from people who don’t want this government to succeed.”
Far from being a political Austin Powers, sapped of his vitality by an invisible enemy, Mr. Johnson said he had lost 26 pounds since his recovery. Having long struggled with his weight, he has declared himself as “fit as a butcher’s dog” and challenged the people of Britain to join him in getting into shape.
“I could refute these critics of my athletic abilities in any way they want: arm-wrestle, leg-wrestle, Cumberland wrestle, sprint-off, you name it,” Mr. Johnson said, sounding a bit like Mr. Trump, who despite being 74 and moderately obese attributed his recovery to the fact that he is a “perfect physical specimen.”
Both leaders sought to make political points after being discharged from the hospital: Mr. Trump about the miracle-cure qualities of the drugs he was treated with, which he promised to distribute free to all Americans; and Mr. Johnson about the miracle workers who treated him — the doctors and nurses of the National Health Service, perhaps Britain’s most revered institution.
But Mr. Johnson, unlike Mr. Trump, emerged from his illness with a new appreciation for the virus’s deadliness and his own vulnerability. He spoke movingly about how the nurses in the I.C.U. took turns giving him oxygen, something that Mr. Trump, who also received supplemental oxygen, has not mentioned.
Mr. Johnson also became a reluctant proponent of protective measures, a stance that has put him at odds not only with Mr. Trump, but also with members of his own party who worry about the damage that lockdowns do to the economy.
The prime minister’s speech to the Conservative conference was a concession to the times. Whereas he would typically deliver the speech in a giant hall with the party faithful arrayed before him, Mr. Johnson instead faced a camera in an empty room. “There is no one to clap or heckle,” he lamented.
He did his best to turn the page, sketching out his vision of a post-Covid future for Britain: ambitious investments in wind turbines and windmills, under the slogan “Build Back Better,” which happens to also be the slogan of the jobs and recovery plan of former Vice President Joseph R. Biden Jr., the Democratic candidate for president.
The Trump campaign accused Mr. Biden of plagiarizing Mr. Johnson. But “Build Back Better” has been used recently by the United Nations, the World Economic Forum and Prime Minister Justin Trudeau of Canada, suggesting a lack of imagination more than a theft of intellectual property.
In any event, the British news media largely ignored “Build Back Better” and kept the focus on Mr. Johnson’s misplaced mojo. The state of his health is hard to judge, given that his office provided sketchy, uninformative updates while he was sick and has not offered a medical briefing since then. He looked energetic on Tuesday but has seemed occasionally lethargic during debates in Parliament.
“His party conference speech was palpably a chance to shake off the sense that he’s half the man he used to be, that he’s lost his élan and brio, that he’s now a poor shuddering wreck,” said Andrew Gimson, one of Mr. Johnson’s biographers.
“But he hasn’t been able to shake it off,” Mr. Gimson said. “There are a lot of columnists who are committed to the idea that he’s an utter scoundrel, and they write these things partly to convince themselves.”
Still, it is not just Mr. Johnson’s polarizing personality that has caused his problems. His government’s botched response to the pandemic — from its tardy lockdown and trouble-prone test-and-trace system to its serial reversals on lockdown measures — has cemented the perception that it is ill-equipped to deal with the challenge.
Mr. Johnson’s approval rating, which peaked at 66 percent when he left the I.C.U., has sagged to 35 percent, according to the research group YouGov. Early polls suggest that Mr. Trump may not even get that transitory a sympathy bump from his illness, and unlike Mr. Johnson, he is due to face voters in less than a month.
When Mr. Johnson and several of his top advisers got sick in late March, it was eerily similar to the contagion now sweeping through the White House. Like the president’s aides in the West Wing, Mr. Johnson and his staff huddled in the cramped offices of 10 Downing Street, not observing adequate social distancing.
What it revealed, people who know him said, was Mr. Johnson’s blithe disregard for health issues — another trait he once shared with Mr. Trump. Before his illness, he boasted of his appetite for cheese and argued against regulating fast-food advertising or taxing companies that use unhealthy ingredients.
“He wasn’t really suited for this kind of problem,” Mr. Gimson said, “because he’s never taken health problems seriously.”