Hillary Clinton’s well-publicized near collapse following a Sept. 11 memorial event earlier this month has accelerated discussion around the 68-year-old democratic presidential candidate’s health and how it might affect her ability to hold the office of president.

The incident was attributed to a bout of pneumonia and dehydration for which she had been undergoing treatment. Clinton appeared later in the day, saying she felt great, and has since resumed campaign activities.

Clinton’s Republican opponent, Donald Trump, has raised several questions in recent months about Clinton’s health. While pneumonia is likely a transient health concern for Clinton, perhaps more alarming is her history of blood clots going back nearly 20 years. In 2012, Clinton suffered a concussion after hitting her head during a fainting episode associated with dehydration related to a stomach virus. A follow-up MRI discovered a blood clot for which Clinton continues to receive treatment with anticoagulants.

Trump, 70, may find it advantageous to highlight Clinton’s health history because his own health reports have been relatively clean. Aside from being a few pounds overweight and taking medication to reduce cholesterol, Trump’s health history appears unremarkable.

Some experts have recommended both candidates undergo a neurological assessment as they are in the age range during which Alzheimer’s disease and other forms of dementia become evident.

Whether Clinton’s health concerns or Trump’s apparent lack of health concerns make one or the other more fit to hold the office of president is an interesting question. Plenty of candidates with questionable health histories have ascended to the office of the president and carried out their terms without incident. Other U.S. presidents suffered health problems and illnesses while in office, which led to questions about presidential succession, a concept that was poorly defined by the constitutional framers.

William Taft, for example, was morbidly obese, which likely contributed to sleep apnea and led to bouts of falling asleep during presidential meetings. On a more serious note, some experts speculate Ronald Reagan was already suffering the effects of Alzheimer’s disease late in his presidential term.

Following are several presidents whose health maladies came into play during the presidential terms and could have impacted the course of history:

Churchill, Roosevelt, Stalin

In this Feb. 12, 1945, file photo, Prime Minister Winston Churchill, left, smokes a cigar while meeting with President Franklin D. Roosevelt, center, and Russian Marshal Josef Stalin, at the Livadia Palace gardens in Yalta. Roosevelt went to great lengths not to be photographed in any way that showed his disability. (AP Photo)

Franklin Delano Roosevelt

Perhaps the most notable and well-known presidential malady was Franklin Delano Roosevelt’s polio. The four-term president contracted infantile paralysis, or polio, in 1921 when he was 39 years old. While on vacation with family at Campobello Island, the future president began to experience lower back pain, weakness and the inability to hold his own weight.

Dr. Robert Lovett diagnosed Roosevelt with polio after several other possibilities were explored and dismissed. At the time, there was no cure for polio, which rarely struck adults. Roosevelt believed that the rigors of politics may have weakened his immune system, leaving him susceptible to contracting the disease.

Roosevelt removed himself from politics and shifted his attention during the next several years to rehabilitation, which eventually paid off. He regained strength in his arms and back and learned to stand with the help of leg braces.

Roosevelt’s disability did not directly affect his ability to function as president, but he was generally uncomfortable allowing the publicly to see him as disabled. As such, rather than remain bound to his wheelchair during appearances, he devised a way of walking with support to podiums, and the press largely complied with the president’s wish not to be photographed walking or being transferred to and from his wheelchair.

Despite his disability, Roosevelt was viewed by the American people and throughout the world as a symbol of strength.

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Grover Cleveland tumor

A bottle which holds a lesion taken from President Grover Cleveland’s mouth is seen at the exhibition “When the President is the Patient,” at the College of Physicians in Philadelphia in 2000. The exhibition displayed some of the oddities of presidential medicine that includes items such as a wax replica of the blistered open sore that nearly killed George Washington and the blood-stained collar worn by Abraham Lincoln the night he was assassinated. (Photo: Misha Kwasniewski/AP Photo)

Grover Cleveland

In 1893, Grover Cleveland discovered an unusual lesion on the roof of his mouth which turned out to be malignant. Surgeons who were consulted about what to do for the lesion recommended surgery.

But the country was in the midst of a depression, and the president was leading a movement to repeal the Sherman Silver Purchase Act to uphold the gold standard. He was concerned that news of his condition might create public concern during an already unsettled time, so he elected to have the surgery done secretly.

To keep the surgery hidden from public view, surgeons removed the lesion aboard a yacht on July 1, 1893, as it sailed from New York to the president’s summer home on Buzzards Bay in Massachusetts. The surgery removed the lesion along with two teeth and part of Cleveland’s palate, which was reconstructed to help minimize the impact on his speech.

Despite the surgery’s success from a medical point of view, Cleveland never seemed to fully recover and dealt with hearing loss, irritability and depression for the remainder of his time in office.

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Woodrow Wilson

Although he already had already suffered two strokes, Woodrow Wilson went on to be elected president. He suffered additional strokes while in office. Here, surrounded by crowds, President Woodrow Wilson appears healthy as he throws out the first ball at a baseball game in Washington in 1916. (AP Photo)

Woodrow Wilson

Woodrow Wilson had a history of cerebrovascular disorders pre-dating his election to the presidency. A stroke in 1896 left him with loss of dexterity in his right hand along with numbness and pain in his hand and arm. In 1906, he suffered a second stroke that affected his vision. Several doctors urged Wilson to adopt a more sedentary lifestyle, but the future president found it difficult to withdraw from his ambitions.

His spotty health history didn’t stop Wilson from being elected president in 1912, but shortly after taking office, he suffered his third stroke, which affected Wilson’s left arm. Some doctors recommended rest while others ominously predicted he would not survive his term.

In 1919, Wilson collapsed while on a public speaking tour in Pueblo, Colorado. Upon his return to Washington he suffered his most severe stroke at the White House, which left him partially paralyzed.

A purported cover-up ensued, aided by a collaboration between Wilson’s doctor and the first lady, who largely concealed the extent of the president’s condition and would not officially declare him disabled when questions of succession came up in Congress.

The remainder of Wilson’s term was spent bedridden or in a wheelchair, with few public appearances that would betray the severity of his condition. His wife, Edith, selected which messages he would receive and delegated others to his cabinet.

Wilson survived his presidency but the circumstances surrounding his condition in the waning days of his presidency helped pave the way for the 25th amendment, which spells out succession to the presidency in cases of illness and disability.

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JFK

While President John F. Kennedy’s public image was one of youth and vitality, behind the scenes he dealt with crippling back pain and other ailments. Here, Kennedy walks with Secretary of Defense Robert McNamara toward a pier on Cape Cod to board the Kennedy family boat for an outing in 1961. (Photo: John Rous/AP Photo)

John F. Kennedy

The picture of youthful vitality, John F. Kennedy was secretly suffering a variety of ailments during his presidency that the public was unaware of.

The president suffered chronic low back pain, perhaps triggered by a sports injury during his youth. Doctors attempted to help ease his back pain via a surgical procedure in 1954 that left him near death due to septicemia. After that, he focused on nonsurgical therapies, took hot baths several times a day, wore a back brace and used crutches when not in public.

Kennedy also suffered several other maladies, which were kept hidden from the public eye, including Addison’s disease, irritable bowel syndrome and allergies. While president, Kennedy took a variety of medications including steroids for his Addison’s disease, painkillers for his back, anti-spasmodics for colitis and antihistamine for allergies.

Some speculate Kennedy’s ailments may actually have contributed to his assassination. Biographers have noted that after the first bullet struck him in the neck, his back brace kept him upright and allowed the next bullet to fatally strike him in the head.

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Lincoln

Not event the president of the United States could avoid contracting the dreaded small pox virus, which caused him to become gravely ill. This undated illustration depicts the president making his Gettysburg Address in 1863, at which time he was already showing symptoms of the disease. (AP Photo)

Abraham Lincoln

The Gettysburg Address is perhaps one of Abraham Lincoln’s most famous presidential moments, but few know what happened in the days following that speech.

On the train ride back to Washington from Gettysburg, Lincoln developed a fever, headache and weakness, symptoms which progressed upon his return to the White House. On the fourth day of his illness, Lincoln developed a blistering rash. A doctor declared him to have “a touch of the varioloid,” the 19th century term for small pox.

Lincoln quipped in return, “For once in my life as president, I find myself in a position to give everybody something.”

Although vaccination programs had begun to limit the deadliness of small pox by the time Lincoln contracted the disease in 1863, the president’s condition was guarded for several days and many close aides anxiously wondered what would become of the war-torn country should Lincoln succumb to the disease.

But Lincoln turned the corner after about a week of illness and by mid-December, although he remained weak and emaciated, he was able to attend a play at Ford’s Theater.

One of Lincoln’s servants was not so lucky. He contracted the disease, perhaps from Lincoln or perhaps from one of the many other people who were sick with the disease in Washington at the time, and died early in 1964.

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Eisenhower

President Dwight Eisenhower, back in Washington from Denver where he suffered a heart attack on Sep. 24, 1955, gives a speech as thousands of well-wishers gave him a roaring “Welcome home” at National Airport on Nov. 11, 1955. Mamie Eisenhower is at left and Vice President Richard Nixon at right. (AP Photo)

Dwight Eisenhower

In April, 1955, Dwight Eisenhower summoned his personal physician to his bedside, complaining of chest pain. Ike was on vacation in Denver at the time and went to bed early one evening feeling sick following a round of golf earlier in the day. He woke up in the middle of the night feeling ill and chalked it up to gastrointestinal distress caused by eating a hamburger with onions the previous day.

Twelve hours later, however, the pain recurred and the president was rushed to Fitzsimmons Army Hospital where it was determined he was having a heart attack. Unlike many other presidential maladies, Eisenhower’s condition was not hidden from the public. Frequent updates were provided to the public, and the president even appeared during a photo opportunity sitting in a wheelchair and wearing pajamas that included five stars on each collar, denoting his previous Army rank, along with a sixth gold star that he joked his doctor awarded him for good conduct while hospitalized.

Eisenhower remained hospitalized for more than a month before he was released, retreating to his farm in Gettysburg, Pennsylvania, for additional rest and recuperation. He was re-elected to a second term as president just one year following his heart attack.

During his second term, Eisenhower suffered a mild stroke but quickly recovered.

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