LONDON — President Trump’s disclosure that he had been infected by the coronavirus sent a shudder around the world on Friday, drawing sympathy from leaders who have grappled with the pandemic in their own countries and more pointed responses from critics who noted Mr. Trump’s cavalier handling of the threat.
Mr. Trump is not the first world leader to be stricken. Prime Minister Boris Johnson of Britain and President Jair Bolsonaro of Brazil both were infected — drawing an eerie link between three populist politicians whose countries have been particularly hard hit by the pandemic.
At 74, Mr. Trump is older and more vulnerable than either of those men. The news of an American president contracting a potentially lethal virus also carried global repercussions beyond what would be generated by any other world leader. Financial markets fell in Asia and wobbled in Europe and the United States, before steadying after the disclosure that Vice President Mike Pence had tested negative.
For allies and adversaries alike, there was a sense of shock as they woke up to the news on Friday — even after three and a half years in which many believed they had lost the capacity to be shocked by anything involving a president whose words and deeds have regularly rocked the international order.
From Mr. Johnson to President Vladimir V. Putin of Russia to Chancellor Angela Merkel of Germany, a host of foreign leaders voiced concern, sending Mr. Trump good wishes for his convalescence, as well as that of the first lady, Melania Trump, who was also infected.
“Hope they both have a speedy recovery from coronavirus,” Mr. Johnson said on Twitter, making no mention of his own bout with Covid-19, which sent him to an intensive-care unit where, he said later, “things could have gone either way.”
Mr. Putin, who has taken extraordinary precautions to shield himself during the pandemic, told Mr. Trump by telegram, “I am certain that your inherent vitality, good spirits and optimism will help you cope with this dangerous virus.”
Beyond the expressions of sympathy, however, there was an unmistakable sense of “I told you so,” particularly in countries that have practiced social distancing more assiduously than has much of the United States.
Mr. Trump, these critics noted, had minimized the threat of the virus, spurned simple precautions like wearing a mask and taken risks like holding campaign rallies with little or no social distancing and few if any masks. During the presidential debate on Tuesday, he mocked former Vice President Joseph R. Biden Jr. for wearing a mask.
“If you look at all his public campaigns, there are lots of people who gather without masks,” said Kenichiro Sasae, a former Japanese ambassador to Washington. Mr. Trump, he said, “had given the impression that he’s trying to open the economy first.”
In China, which Mr. Trump has blamed as the seedbed of the virus, the commentary reflected a mix of sympathy, disbelief and even celebration from some who saw the development as just retribution for Mr. Trump.
“The whole world rejoices!” read one comment on Sina Weibo, a popular though heavily censored social media platform, which was liked 55,000 times in the hour after it was posted.
Others took the opportunity to ridicule Mr. Trump. Radoslaw Sikorski, a former foreign minister of Poland, wrote on Twitter, “Mr. President @realDonaldTrump, I suggest you do not try to treat yourself with bleach.”
For some, Mr. Trump’s misfortune was a grim reminder of a virus that does not distinguish between rich and poor, weak and powerful. Some even saw it as a kind of teachable moment for the world’s most powerful man.
In Myanmar, a Baptist minister who met with Mr. Trump in the Oval Office last year and told him about oppression and torture by the military, said this ordeal could help him better understand the pain of others. “Now, he is suffering himself and he should be compassionate for his people,” said the minister, Hkalam Samson.
Britain’s experience shows that even in a country with a well-organized political system, a leader’s sudden illness can be deeply unsettling. When Mr. Johnson contracted the virus in March, the government was adrift for several days while he struggled to keep leading the response to the pandemic, via Zoom calls, from isolation in his official residence on Downing Street.
When Mr. Johnson, 56, was admitted to the hospital and then to intensive care, he deputized the foreign secretary, Dominic Raab, to act in his absence. But that did little to dispel the uncertainty, especially since unlike in the United States, there is no legal line of succession if a prime minister dies in office or is permanently incapacitated.
The government issued upbeat, unrevealing reports of Mr. Johnson’s health, using phrases like “mild symptoms” and “good spirits” — the same terminology deployed by White House officials on Friday. After Mr. Johnson was released from the hospital on Easter Sunday, he disclosed that his condition had been graver than was reported.
Even now, six months later, politicians in Westminster whisper that Mr. Johnson is not fully back in fighting form, though he insisted earlier this week he was as “as fit as a butcher’s dog,” having lost weight since his illness.
In Brazil, Mr. Bolsonaro’s bout with the virus was less serious. He said he suffered only mild fever and body aches before testing positive on July 7. After quarantining on the grounds of the presidential residence in Brasília, he pronounced himself recovered on July 25, posting a photo of himself smiling and giving a thumbs up.
Mr. Bolsonaro, 65, who has adopted Mr. Trump’s approach of playing down the virus and promoting miracle cures, appeared to brandish a box of hydroxychloroquine pills, the anti-malaria medicine. Despite claims by Mr. Trump, there is growing scientific consensus that the drug is not effective in treating Covid-19.
In the zero-sum world of geopolitics, Mr. Trump’s setback deepens a political and public-health crisis in a country already consumed by the presidential election. Some analysts said they worried that China, Russia, Iran, North Korea or another adversary would try to exploit the disarray in Washington.
“The unanswerable question is whether any country will be tempted to use this period to advance its own agenda on the assumption that the United States will be too preoccupied to respond,” said Richard N. Haass, the president of the Council on Foreign Relations who served in the George W. Bush administration.
Mr. Trump’s erratic style had already been a recurring source of anxiety abroad. Analysts said the major worry was not about continuity of government — given the depth of contingency planning in the United States — but how the president would react to enforced confinement and the specter of illness.
“This highlights that what has always been destabilizing about Trump’s administration is not really his policies — it is him,” said Jeremy Shapiro, an Obama administration national security official who is now research director at the European Council on Foreign Relations. “In this sense, the worry from foreign governments will likely be its effect on the president’s fragile psyche.”
On a day-to-day basis, however, Mr. Trump’s health problems are not likely to affect relations with most countries. His nuclear negotiations with North Korea are paralyzed anyway. And he has just come off a diplomatic coup with the restoration of relations between Israel and Arab countries in the Persian Gulf.
Mr. Trump’s vilification of China has frozen relations with Beijing. His tensions with the European Union over trade and Iran — on top of the distractions of the pandemic — had limited his contact with leaders like Ms. Merkel. She had rebuffed his invitation to a Group of 7 meeting in May.
Gérard Araud, a former French ambassador to Washington, characterized the news as a “blip” in “the brain of our leaders, who have much more urgent issues to handle.” And Kim Darroch, a former British ambassador to the United States, said, “It’s not like Trump was all that great at consulting anyway.”
Mr. Darroch, who resigned his post last year after British newspapers published private cables in which he was bluntly critical of the Trump administration, said close allies like Britain communicated with the United States regularly through military, diplomatic and intelligence channels.
But that does not mean, he said, that people in Britain and elsewhere were not following the news in the United States with keen interest.
“We all care about this because America is the global superpower,” he said.
Reporting was contributed by Mike Ives, Elaine Yu and Yonette Joseph from Hong Kong; Keith Bradsher and Claire Fu from Beijing; Carlos Tejada from Seoul, South Korea; Amy Qin from Taipei, Taiwan; Steven Erlanger from Brussels; Saw Nang from Mandalay, Myanmar; and Richard C. Paddock from Bangkok, Thailand.