Hillary Clinton is the first major party candidate for president in modern American political history to be diagnosed with pneumonia after being named the party’s standard bearer.

Clinton’s physician, Dr. Lisa Bardack, issued a statement late Sunday that the former secretary of state was diagnosed with pneumonia on Friday. That public statement did not come, however, until at least 48 hours after the diagnosis was made and confirmed to Clinton.

Subsequent to that diagnosis, Clinton attended a fundraiser with Barbra Streisand. At that event, Clinton made her now infamous gaffe in which she said half of Donald Trump’s supporters fit in a “basket of deplorables.”

On Sunday, Clinton left a 9-11 memorial event in New York City early and was filmed stumbling as she was helped into an awaiting SUV by her aides. Later in the day, before her diagnosis of pneumonia was announced publicly, Clinton was filmed emerging from her daughter Chelsea’s apartment building in New York City, beckoning for a young girl to come to her, and holding the girl’s shoulders while the two posed for a photograph.

Clinton was scheduled to travel to California this week, but that trip, which her aides said was “up in the air” Sunday afternoon, has now been canceled.

Other presidential candidates during the past century have been ill after receiving their party’s nomination for president, but none has been diagnosed with a serious illness during a presidential campaign and had that illness become an issue in the campaign.

But Hillary Clinton’s health has now become a major issue in the 2016 presidential campaign.

On Sunday, even Chris Cillizza at The Washington Post reported, “Hillary Clinton’s health just became a real issue in the presidential campaign.”

Throughout much of the 20th century, when technology limitations allowed candidates to control the release of personal information to the media and public, presidential candidates were often better able to conceal their health problems.

When Franklin Delano Roosevelt ran for president in 1932 (and subsequently, when he was re-elected in 1936, 1940, and 1944), he suffered from paralysis in his legs and lower body, after he developed polio in 1921.

The extent of his disability was largely concealed from the public. He was sometimes able to deliver speeches while standing at a podium, thanks to heavy braces that encased his legs.

But the lack of transparency about the severity of Roosevelt’s polio was surpassed by the failure of his campaign team to be forthright about the poor state of his health when he ran for re-election in 1944.

As The Boston Globe reported in 2011, “In a remarkable document just released by the Lahey Clinic, Frank Lahey, the clinic’s founder, wrote on July 10, 1944, that he ‘did not believe that, if Mr. Roosevelt were elected President again, he had the physical capacity to complete a term’’’:

Lahey, of course, was right. Roosevelt died from a cerebral hemorrhage on April 12, 1945, just a few months into his new term. Written days before Roosevelt won the Democratic nomination, Lahey’s unflinching diagnosis provides a fascinating footnote to a decisive point in American history, and rare insight into what Roosevelt’s doctors — and presumably Roosevelt himself — knew about his health as he began another presidential run. For decades, the sealed note lay largely hidden from public view, its obscurity lending it a mythic status among the few who believed it existed.

In 1960, Republican nominee Richard Nixon had a knee infection and a fever in late September. Many historians point to his illness as one cause of his poor performance on camera in the first of the four famous Kennedy-Nixon debates that year.

As History.com reported:

On the evening of September 26, when the two candidates arrived at the CBS broadcast facility in downtown Chicago for the first televised presidential debate in American history, Nixon’s streak of bad luck continued. Stepping out of the car, he banged his bad knee and exacerbated his earlier injury. The vice president had recently suffered a bout of the flu and was still running a low fever; he had nonetheless spent a grueling day on the campaign trail and looked drained. Kennedy, meanwhile, had been holed up in a hotel with his aides for an entire weekend, fielding practice questions and resting up for the first of four “Great Debates.”

Ironically, it was Kennedy who had more serious health issues, but those were not reported in the press at the time.

“John F. Kennedy, whose apparent vigor scored him points during the 1960 election, suffered in secret from Addison’s disease, osteoporosis and a host of additional ailments,” History.com reported.

In 1976, incumbent President Gerald Ford developed laryngitis in the final days of the campaign. In fact, he lost his voice, and as a result, it was his wife, Betty Ford, who read her husband’s concession speech on election night.

Some recent articles have claimed that Ronald Reagan’s health was an issue when he ran for president.

“Everybody is wrong when they talk about Reagan’s health being an issue in the presidential campaigns of 1980 and 1984,” presidential historian and Reagan biographer Craig Shirley told Breitbart News in an exclusive interview.

“His age and mental acuity were sometimes discussed, and to the extent they were, it was by liberal journalists with an agenda,” Shirley stated.

Clinton’s diagnosis with pneumonia at the age of 68 is a concern for her own health and her ability to conduct a vigorous campaign between now and election day, which as of Monday is only 57 days away.

According to Medicine.net, “Pneumonia is inflammation of the lung tissue usually but not exclusively caused by infection from bacteria, virus, or fungus”:

Pneumonia causes the air sacs at the end of the airways in the lungs to fill with pus. If inflammation affects both lungs, the infection is termed double pneumonia. If it affects one lung, it is termed single pneumonia. If it affects only a certain lobe of a lung, it’s termed lobar pneumonia. Most pneumonias are caused by bacteria and viruses, but some pneumonias are caused by inhaling toxic chemicals that damage lung tissue. Pneumonia can cause fever, chills, cough, and difficulty breathing. Severe pneumonia can result in death.

“Because pneumonia is caused mainly by infectious microbes, pneumonia can be contagious,” Medicine.net reported.

Subsequent to a diagnosis of pneumonia, standard medical procedure–for the protection of both the patient and anyone who may come in contact with her–recommends isolation and rest.

The usual treatment for a patient of Hillary Clinton’s age who is diagnosed with pneumonia is “rest, antibiotics, fluids,” Dr. Jane Orient, executive director of the Association of American Physicians and Surgeons, told Breitbart News.

“Usually going to crowded outdoor events is not part of the regimen. Most are too sick to get out of bed much,” Dr. Orient said.

As for whether Clinton’s continued presence at campaign events presents a public health risk to those who come in contact with her, Dr. Orient said, “Usually not–but depends on what the organism is.”

The time it will take to recover from pneumonia is “probably a week or two,” she added, noting that it “possibly can linger much longer–varies with [the] individual.”

“The cough has been going on for a long time. Curious that cough did not seem to be part of the day’s problems, at least I haven’t seen it mentioned. It is also curious that she waved and said she felt great when leaving Chelsea’s,” she told Breitbart News.

“I haven’t seen the patient, of course. It’s just that the information we have been given on the events does not seem to fit well with the proffered explanation,” she added.

At least one other national political leader in American history developed pneumonia at the age of 68.

William Henry Harrison, America’s ninth president, died of exhaustion and complications from pneumonia at the age of 68 in 1841, 32 days after he was inaugurated. He developed pneumonia after delivering a lengthy inaugural address on a frigid March day in the nation’s capital.

Hillary Clinton will turn 69 on October 26.