The Democratic nominee's pneumonia, diagnosed on Friday, wasn't disclosed for two days until questions swirled about her early exit from a 9/11 commemoration ceremony and a bystander in Manhattan tweeted footage of her stumbling.
That's a big change from the pre-social media age, when presidents and White House hopefuls were able to keep their maladies under wraps -- or at least muted -- for considerably longer stretches of time.
In 2016, it's a particularly sensitive issue in an already-raucous campaign featuring two candidates who are grandparents. Donald Trump, 70, would be the nation's oldest incoming commander in chief. Clinton, 68, would be a shade younger than Ronald Reagan was when he first took the oath of office.
Which makes the Clinton campaign's non-disclosure about the pneumonia conspicuous.
In the modern media age, "Every time with an illness of a president -- or in this case a candidate -- the immediate reflex is to put out a reassuring statement," said John Milton Cooper, biographer of President Woodrow Wilson, who nearly a century ago spent his final year-and-a-half in the White House largely holed up from public view after suffering a stroke.
Concerns over presidential health are so familiar that they've been fodder for popular culture, memorably dramatized on television in "The West Wing." Character questions about fictional Democratic President Jed Bartlet -- otherwise depicted in the series as a paragon of moral rectitude -- are laid bare by his cover-up of ongoing multiple sclerosis, including complicity by his physician wife.
Back in the real world, not all presidential candidates have been fully coy and deceptive about their medical conditions. In 2008, Republican nominee John McCain gave select members of the media a limited glimpse at his medical records. Based on that, CNN Chief Medical Correspondent Dr. Sanjay Gupta found the Arizona senator former prisoner-of-war in Vietnam, then 72, to be in good health.
Here are highlights -- or arguably lowlights -- of less-than-candid approaches to health by presidents and would-be White House occupants.
President Chester A. Arthur, 1883-84
The 21st President was elevated to the nation's highest office from the vice presidency in 1881, with the assassination of President James Garfield. Expectations were low for Arthur, known primarily as a machine hack who had grown wealthy in a series of GOP patronage jobs.
Arthur, though, surprised many once ensconced in the presidency. He reversed course and moved to assign government jobs to the most qualified applicants, not party insiders. He also held reasonably enlightened views for the day on treatment of minority groups and immigrants.
But his probity didn't extend to health matters. In 1884 Arthur sought, unsuccessfully, the GOP nomination. He omitted that he had Bright's disease, a kidney ailment. By that point rumors about his health had already circulated. He had lost weight, appeared older, and struggled to keep up with the pace of the presidency, even in those more languid days.
"He's essentially dying, and he doesn't live very much longer," said David Pietrusza, author of numerous books about the presidency, White House races and other historical topics.
Arthur died in 1886, about 20 months after the start of the presidential term he sought.
President Grover Cleveland, 1893
The only president to serve non-consecutive terms, Cleveland and his minions undertook one of the most brazen, but little-known, cover-ups of health in White House history.
A former Erie County sheriff, mayor of Buffalo and New York governor, Cleveland won the presidency in a close 1884 contest but was booted from office four years later. He won back the prize in 1892, and Inauguration Day was likely his best moment in office.
"In the spring of 1893, just after he began his second term, Cleveland noticed what he called a 'rough spot' on the roof of his mouth," said Matthew Algeo, author of "The President Is a Sick Man: Wherein the Supposedly Virtuous Grover Cleveland Survives a Secret Surgery at Sea and Vilifies the Courageous Newspaperman Who Dared Expose the Truth."
"His doctor diagnosed it as a cancerous tumor," Algeo said, via email. "But Cleveland didn't want the public to know he was ill. At the time the country was mired in a depression that came to be known as the Panic of 1893. So Cleveland decided to have the surgery performed secretly, on a friend's yacht as it sailed from New York to Cleveland's summer home in Massachusetts. That was in early July 1893. The surgery was a success. It's also worth mentioning that Cleveland guarded his privacy very jealously, and he was loath to have the newspapers discussing his health."
Most disturbing, in hindsight, is the way Cleveland and supporters suppressed the news, Algeo said.
"There were rumors that the president was ill. But Cleveland's surrogates insisted that the president was suffering from nothing more than a toothache. They said he had had minor dental surgery. It took Cleveland several weeks to recuperate at his summer home."
"But at the time it was not all unusual for the president to leave Washington for the summer, so his absence from the White House aroused few suspicions. After he was fitted with a prosthetic device in the roof of his mouth, his normal speaking voice returned and he began appearing in public again. By the time he returned to DC in September, the story had more or less blown over. The truth wouldn't come out until one of the doctors wrote about the surgery in the Saturday Evening Post in 1917 -- long after Cleveland was dead."
President Woodrow Wilson, 1919-21
Wilson was riding high in September 1919. One of the only Democratic presidents of his era, Wilson had led the nation through victory in World War I and hailed in Europe as a hero.
Yet while on a grueling, 8,000-mile, 22-day domestic tour to promote formation of the League of Nations, Wilson suffered a debilitating stroke, in Pueblo, Colorado. He returned to Washington and was never the same physically.
During the waning period of Wilson's presidency, his wife, Edith, kept close guard over visitors, and helped conceal the true extent of his illness and incapacitation. But she wasn't operating alone. Dr. Cary T. Grayson, was a constant presence at the president's side — at a time that attending physicians didn't trail presidents 24 hours a day.
"They isolated him. That was medical wisdom at the time," said Cooper, the Wilson biographer and professor emeritus at the University of Wisconsin. "Now, of course, it's exactly the opposite. You try to get stroke victims back into social interaction as soon as possible."
Wilson regained some of his health, but the stroke's lasting effects -- he remained partially paralyzed on one side -- made him a less effective president. The League of Nations proposal didn't get through Congress, controlled by Republicans. Wilson died in early 1924, less than three years after leaving office.
President Franklin Delano Roosevelt, 1944-45
FDR's public career was, in a sense, a case of less-than-leveling with the American public about his health issues. Having contracted polio at age 39, his inability to walk was well, but not universally, known.
But on his way to winning the presidency -- and through his dozen years in the White House -- Roosevelt's handlers were careful to prevent the president from being photographed in a wheelchair. In a more gentile age of press relations -- through the national crises of the Great Depression and World War II -- journalists largely went along.
Roosevelt's health situation, though, became more acute as the Allies marched toward victory. In early 1945, he delivered the State of the Union speech sitting down, said Pietrusza, the presidential historian. Then conferring with Winston Churchill and Joseph Stalin at the Black Sea port of Yalta, many observers commented on the president's ill state of health.
Having traveled more than 7,000 miles and already in physical decline due to what his personal physician diagnosed as hardening of the arteries, FDR used his dwindling energy tying to cajole Stalin into joining the US in the Pacific war against Japan.
"At Yalta he's turning literally green," Pietrusza said. Departing the conference in February, Roosevelt died of a stroke two months later.
Richard Nixon and John F. Kennedy, 1960
Though hiding health conditions by would-be presidents can hurt, sometimes excess candor is even worse.
Vice President Richard Nixon learned this in 1960 when seeking the White House himself. The Republican nominee injured his knee while exiting a car in North Carolina, a condition that subsided briefly but then flared up during a bowling excursion at Camp David.
Then in an unfortunate bit of timing Nixon stumbled again while traveling to Chicago for one of four televised debates against his Democratic rival, Sen. John F. Kennedy of Massachusetts. Nixon played through pain that night but the knee injury contributed to the perception among many that he lost to telegenic opponent JFK.
The Nixon campaign didn't try to hide the extent of his injury -- including a week-long hospitalization. It gave Kennedy, only a few years younger, a crucial opening to exploit. "Losing a week in a campaign, under any circumstances, is troublesome," Pietrusza said.
JFK ended up winning that race, in the closest popular vote result in American history. But he was hardly a figure to emulate when it came to candor about his health.
Though not revealed until years, often decades, after his assassination in 1963, the President suffered from a series of physical maladies. Frequently in the hospital as a child and teen, Kennedy had been hospitalized in 1954 -- and was deemed so ill that he was actually administered last rites by a priest.
The Kennedy White House would go on the be arguably the least transparent in modern history about the president's health. A 2003 Kennedy biography by historian Robert Dallek -- conducted with a medical consultant -- found that the president suffered from ailments far more extensive, was in deeper pain, and took a larger array of medications, than was previously revealed.
Paul Tsongas, 1992 Democratic presidential candidate
It's one of the most iconic pieces of presidential campaign footage in recent decades. A 50-year-old man in seeming robust health swims butterfly strokes in a pool.
The candidate, presidential hopeful Paul Tsongas, wasn't just showing of his aquatic moves. The campaign of 1992 Democratic primary candidate sought to portray him as an exemplar of stellar health, after a cancer bout forced him to retire from the Senate in 1985, after only a single term.
Tsongas made his survival from non-Hodgkin's lymphoma, a slow-growing cancer of the lymph system, an issue in his presidential campaign. Tsongas, though, lost that race to then-Arkansas Gov. Bill Clinton.
Still, Tsongas became known as much for his health condition as policy prescriptions. On the campaign trail Tsongas, under questioning, revealed that he had been treated in 1987 for a recurrence of the lymphoma. Months after exiting the race Tsongas said he had erred in not disclosing the recurrence.
He pledged that if he ever ran again, he would submit his medical records to independent experts.
Tsongas passed away in January 1997, two days before the end of the White House term which he was seeking.