In 1960, Richard Nixon spent a stint in the hospital recuperating from a knee injury that occurred during his ambitious and perhaps foolish gambit to travel to all 50 states during the presidential race.

In the spring of 1992, a raspy Bill Clinton was ordered off the campaign trail by doctors, scrapping a major economic address due to a nagging battle with laryngitis.

And during the 2000 campaign, Bill Bradley canceled events in California and went to the hospital for an irregular heartbeat.

A presidential candidate suffering from an illness or ailment is certainly nothing new. The campaign trail has always been an unforgiving grind, and the dizzying array of modern-day demands are more grueling than ever before. It's taxing, it's exhausting and it's what White House hopefuls signed up for.

So the revelation of Hillary Clinton's bout with pneumonia, which contributed to her leaving a Sept. 11 memorial event Sunday and will take her off the campaign trail for at least a couple days this week, is in itself not particularly startling. Seventeen straight months of overloaded itineraries that begin before dawn and often end in the evening on a plane in the sky are bound to take a physical toll on anyone, let alone aspirants in their 60s and 70s.

The problem for Clinton is that she attempted to conceal her illness. Once again, she has been found not being fully transparent in order to protect her own delicate political prospects, a recurring offense that will only exacerbate her trust deficit with the public.

"We could've done better yesterday," Clinton spokeswoman Jennifer Palmieri tweeted in response to mounting criticism, "but it is a fact that [the] public knows more about HRC than any nominee in history."

We could have done better yesterday, but it is a fact that public knows more about HRC than any nominee in history. https://t.co/Q50oHK85wQ — Jennifer Palmieri (@jmpalmieri) September 12, 2016

That response in itself accentuates the larger problem confronting Clinton in the homestretch of the 2016 race. As one of the most recognized and vetted people on the planet, there's still a significant portion of the American electorate that feels like they know her well enough not to trust her.

Conspiracy theories and unfounded speculation about Clinton's health were already rushing prominently through conservative media outlets and in private watercooler conversations at the office and around the bar. Then, one of the most simple and common signs of sickness kicked those suspicions to a new level.

Clinton endured a coughing fit during a campaign stop in Cleveland last Monday. Reporters published stories about it. The campaign attributed it to allergies.

Nick Merrill, Clinton's traveling press secretary, even launched a dismissive dis of one NBC News reporter, tweeting at him "to get a life."

But it happened again later that day on her campaign plane during a gaggle with reporters. This coughing episode continued for so long she had to briefly excuse herself from remarks criticizing Donald Trump's affinity for Russian President Vladimir Putin.

Clinton soldiered through a nationally televised commander-in-chief forum on Wednesday night without incident and continued campaigning in Charlotte, North Carolina, and Kansas City, Missouri. On Friday, when she appeared before cameras after a private national security briefing, she looked drained and sounded spent. She carefully restrained her voice, as if to avoid provoking any irritation that would incite an outburst.

This is the day Clinton's doctor diagnosed her with pneumonia, a leading cause of hospitalizations in the U.S. But instead of coming clean with this information immediately, the Clinton campaign made the decision to hold it back, as it inherently prefers to. It's not dissimilar to the lingering controversy over her private email server, in which the Clinton campaign insisted it had turned over all relevant emails to the State Department in 2014, even though an FBI probe uncovered thousands of additional documents.

David Axelrod, President Barack Obama's former top political adviser, has termed the Clinton campaign's secrecy "a penchant for privacy that repeatedly creates unnecessary problems."

The Clinton campaign well understood the wild and unsubstantiated claims about her health: that she faked a concussion in 2012 to avoid testifying about the Benghazi attacks, that she could be wearing a defibrillator under her jacket and that she suffers from seizures.

If anything, that should've given them more incentive to get out in front of a story that would only look worse if concealed.

Then came Sunday, when Clinton appeared disturbingly wobbly and almost collapsed while waiting to board a black van to escort her away from a Sept. 11 memorial service in New York City. Her knees appeared to begin to give out as her security detail held on to stabilize her.

The image handed skeptics another reason to disbelieve her personal physician's original prognosis that "she is in excellent physical condition and fit to serve as president of the United States."

It also forced the Clinton campaign's hand. Initially, aides did not mention pneumonia as part of the explanation for the candidate's exit. Later, they released a statement from Clinton's doctor, Lisa Bardack, that said the Democratic nominee had been put on antibiotics for pneumonia and was advised to rest and modify her schedule. The prolonged cough, Bardack said, had been related to allergies.

Clinton's campaign canceled a fundraising trip to California planned for Monday and Tuesday, and she is next scheduled to appear in public at a campaign event in Las Vegas on Wednesday.

But her team's attempts to mask the pneumonia and then spin the near-fainting spell will only keep the issue alive longer than it had to be.

The next time Clinton faces the press she will be forced to endure questions like, "What induced the fainting?" "Did you ever lose consciousness?" and "Why didn't you go to the hospital?"