(CNN) As President Donald Trump settles back into the White House after days of experimental Covid-19 treatments at Walter Reed National Military Medical Center, the nation remains bewildered: Just how sick is the President of the United States?
Trump's doctors have been reticent about disclosing too many details of his illness, even allowing him to return to the White House despite saying "he may not be entirely out of the woods yet."
At 74, Trump's age puts him in one of the highest risk groups for severe, even deadly, complications of Covid-19. Obesity and high cholesterol, for which he takes a statin, also raises his risk. It's also well known that the President has a preference for fast food and gets little exercise outside an occasional round of golf.
Many people with Covid-19 who initially appeared to recover have then taken a sudden turn for the worse, requiring hospitalization and the use of ventilators. Trump's doctors will be on the lookout for pneumonia, blood clots, bacterial infections, a sudden drop in oxygen levels and other known complications of Covid-19 over the next days to weeks.
Trump has made it clear that he does not want the nation to see him as weak or fragile before the November election, despite having a deadly illness that has killed more than a million people worldwide so far, including more than 210,000 Americans.
"Now I'm better and maybe I'm immune? I don't know. But don't let it dominate your lives," Trump said in a video taped upon his return to the White House.
A new CNN Poll conducted while Trump was in the hospital found 69% of Americans said they trusted little of what they heard from the White House about the President's health. Only 12% said they trusted almost all of what they heard.
Considering the history of efforts to hide presidential health scares from the public, skepticism is not surprising.
"Presidents have been always worried about showing bad health," CNN presidential historian Douglas Brinkley told CNN anchor Don Lemon on Friday night.
"Woodrow Wilson had a stroke, they covered it up. FDR covered up a lot of health things," Brinkley said.
But Americans today have made it clear they want to know the truth about the health of their commander in chief, he added.
"Since the '80s, we've been very vigilant on medical records, tell us what's going on, we demand to know, there's no more ... Woodrow Wilson-era cover-ups allowed," Brinkley said. "We, as a public, are demanding more."
History reveals an astounding list of hidden truths when it comes to the health of American Presidents.
Grover Cleveland: One of the most unusual was Grover Cleveland's 1893 cover-up of his oral cancer surgery. He smuggled a surgeon and his team onto a friend's yacht to remove a tumor from the roof of his mouth. Cleveland emerged from his "fishing trip" a week later. No one knew what had happened for nearly a quarter century.
Woodrow Wilson: Wilson had suffered several strokes while he was serving as president of Princeton University, years before he ran for President of the United States, Dr. Jerrold Post, coauthor of "When Illness Strikes the Leader," told CNN in a prior interview.
Elected in 1913, Wilson never revealed his medical history to voters, said Post, who is also a professor emeritus of psychiatry, political psychology and international affairs at George Washington University.
In 1919, while campaigning for the Treaty of Versailles, Wilson "suffered a massive stroke, but they concealed it and just said he was under the weather and no one was informed," Post said.
"So we've already had the first woman president, his wife Edith. In fact, she was to have said, 'I don't know why you men make such a fuss, I had no trouble running the country while Woody was sick.'"
Wilson, like Trump, also downplayed a pandemic -- the highly infectious and deadly 1918 flu -- which spread among American troops during World War I and across the US, killing 675,000 Americans and tens of millions around the world.
And Wilson, like Trump, also caught the virus. Despite a severe cough and hallucinations, Wilson was successful in hiding his illness from the public.
"Wilson never made a public statement about the pandemic. Never," said John M. Barry, author of "The Great Influenza: The Story of the Deadliest Pandemic in History," in a prior CNN interview.
"To keep morale up during the war, the government lied. National public health leaders said things like, 'This is ordinary influenza by another name.' They tried to minimize it. As a result, more people died than would have otherwise," Barry said.
Franklin Delano Roosevelt: While the public knew FDR used a wheelchair due to polio when he ran for President for the fourth time in 1944, they did not know he had advanced heart disease and hypertension, said George Annas, chair of the department of health law, bioethics and human rights at Boston University School of Public Health.
Those conditions may have contributed to the cerebral hemorrhage that killed him months into his final term, Annas said.
"The idea of a president dying in office from a disease he knew he had before he ran for election or re-election doesn't sit quite right with most people," Annas said in a prior CNN interview.
Dwight D. Eisenhower: In September 1955, Eisenhower was misdiagnosed with a gastrointestinal issue before doctors discovered he'd actually had a heart attack. Despite the fact that he spent weeks in the hospital, staff at the White House initially downplayed the severity of the heart attack to the public.
Battling claims he'd be unfit to serve another term, Eisenhower won reelection in 1956, undergoing surgery for Crohn's disease later that year and suffering a stroke in 1957, which was reported in the press.
John F. Kennedy: At 43, JFK was the youngest man to become President. He was viewed as healthy and vibrant during his campaign, but in reality, he took office suffering from hypothyroidism, back pain and Addison's disease and was on a daily dose of steroids and a host of other drugs.
"Addison's disease affects your cortisol levels, your ability to handle stress," said Dr. Connie Mariano, who served as White House physician for Presidents George W. Bush and Bill Clinton, in a prior CNN interview.
"You wonder, was the Bay of Pigs an issue because he wasn't adequately treated for Addison's?"
Kennedy also suffered from lifelong back pain and underwent numerous back surgeries during his rise to the presidency. To cope, he wore a tightly laced back brace. A 2017 study of historical documents found the brace may have contributed to Kennedy's death that fateful day in Dallas in 1963 -- the stiff brace may have kept him from recoiling to the floor of his car after the assassin's first bullet to the neck, setting him up for the kill shot.
"I was taken aback by the depth of Kennedy's pain," said neurosurgeon Dr. Justin Dowdy, a co-author of the study, in a prior CNN interview.
"How long he dealt with pain despite his short life, how it affected his life and how they were able to conceal most of that from the public and certainly from his political adversaries," Dowdy said.
Ronald Reagan: Reagan was diagnosed with Alzheimer's after his presidency. Whether it affected his ability to function while in office is a subject of debate. Today, however, medical science knows Alzheimer's begins in the brain 20 to 30 years before symptoms begin.
"Can you rely on the politician's physician to spot these types of issues? Some illnesses are only known by the symptoms the patient complains of," Post said. "The softening of mental processes that begin in early Alzheimer's, for example, may only show up if the politician complains about it."
George McGovern's vice presidential nominee, Thomas Eagleton, had to drop out of the 1972 presidential race when word leaked that he'd undergone electroshock therapy for clinical depression in the 1960s. Critics questioned his ability to govern if he suffered a recurrence of depression.
However, a 2006 study by Duke University psychiatrists applied today's diagnostic criteria to historical records of the first 37 presidents between 1776 and 1974 and found 18 of them met the criteria for psychiatric disorders, mostly depression, anxiety, bipolar disorder or alcohol abuse and dependence.
In fact, the researchers said, 10 of the 18 presidents exhibited enough symptoms of mental illness while in office to have affected their ability to lead the nation.
This is not the first time Trump has dodged questions about his health. While running for president in 2015, he dictated a glowing letter about his physical prowess to his personal physician at the time, Dr. Harold Bornstein. The letter, which was released as a doctor's evaluation of Trump's health, said his "physical strength and stamina are extraordinary."
"If elected, Mr. Trump, I can state unequivocally, will be the healthiest individual ever elected to the presidency," said the letter signed by Bornstein.
"He dictated that whole letter. I didn't write that letter," Bornstein told CNN more than two years later. "I just made it up as I went along."
Updates on Trump's health have been spotty while he has been in office -- even the results of yearly physicals leave unanswered questions -- including details about Trump's unannounced visit to Walter Reed National Military Medical Center last year.
CNN Chief Medical Correspondent Dr. Sanjay Gupta wrote at the time: "As both a physician and a reporter who has covered four administrations, none of this adds up, and it raises the question: What do we really know about President Trump's health?"