During the Watergate scandal, a pithy lesson emerged from the Nixon White House's attempts to obfuscate its connections to the break-in at Democratic Party headquarters: It's not the crime, it's the cover-up.

Decades later, Bill Clinton learned that lesson the hard way when he tried to keep his sexual affair with Monica Lewinsky from going public. He wagged his fingers in the camera in an infamous press conference, declaring that "I never had sexual relations with that woman." Hillary Clinton claimed that allegations against her husband were lies spun by a "vast right-wing conspiracy." The denials ended in humiliation when Ken Starr's office found Lewinsky's blue dress, forcing President Clinton into accepting a plea bargain that suspended his ability to practice law and forever stained his legacy.

For Bill Clinton, the cover-up was far more damaging than the behavior itself. The American electorate was prepared to forgive marital indiscretions in office, but lying to voters' faces created damage that persists to this day. You might think that the Clintons would have learned from those experiences. But events over the last week proved that some politicians remain impervious to the lessons of history, even when it explicitly involves them.

Questions about the health of both presidential nominees have been raised by many critics and commentators. But a series of public coughing fits over the last few weeks have focused most of the attention on Hillary Clinton. When questions arose, mainly from partisans opposed to her candidacy, the Clinton campaign cited allergies as the issue and castigated the partisans for conspiratorial thinking. The media professed its profound disinterest in the question of health, despite making a big issue of it in 2008 with Republican nominee John McCain. Last week, The Washington Post's Chris Cillizza, one of those who demanded detailed medical information from McCain, wondered: "Can we just stop talking about Hillary Clinton's health now?"

Then on Sunday, Clinton collapsed while leaving a 9/11 memorial event early. The Clinton campaign refused to make any statement about her health except that she had "overheated" and needed to rehydrate. Clinton emerged from her daughter's flat in Manhattan later in the day and hugged a child, proclaiming herself well, only to be followed hours later with cancellations of two days' events in California — and an admission by her physician that Clinton had been diagnosed with pneumonia two days earlier.

Needless to say, this raises some questions about Clinton's general health, although pneumonia itself generally presents few problems for otherwise healthy adults, even at Clinton's age. The unsettling video of her collapse at least raises the possibility that this was no minor problem, and reminded voters of the age of both candidates. Cillizza acknowledged that concerns over Clinton's health had become legitimate, and the rest of the news media abandoned their scornful distance on the issue to start asking serious questions about the timing of the diagnosis and its implications.

This episode raises even more profound questions than those about Clinton's physical health, however. Former Obama adviser David Axelrod, at times an ally and an opponent of Clinton, struck close to the heart of the issue Monday morning. "Antibiotics can take care of pneumonia," Axelrod wrote on Twitter. "What's the cure for an unhealthy penchant for privacy that repeatedly creates unnecessary problems?"

The real danger of this fainting spell and the shifting explanations is that it will remind voters of all the serial misrepresentations and flat-out lies told by the Clintons during their quarter century on the national stage. The issues surrounding those dishonesties held varying significance for voters; Whitewater bored them, and the Lewinsky saga mainly titillated them. The email scandal turned into a much bigger problem for Clinton precisely because she stonewalled, then later got caught telling lies about it — and then got caught lying about the FBI's conclusions that exposed those claims of innocence as false.

However, the email scandal and its relation to the Federal Records Act, Freedom of Information Act, and 18 USC 793 probably seemed more esoteric than essential to most voters. Lying on these issues might demonstrate an integrity gap, but it doesn't have real consequences for the lives of most voters.

Presidential health, on the other hand, will hit voters much more directly. They understand the need to minimize the risk of an unforeseen White House transition in times of crisis, and that makes the health of the candidates much more relevant — and much more relatable. The Clintons and her campaign covered up a pneumonia diagnosis while scoffing at perfectly valid questions about her health. This reinforces what NBC News calls Clinton's "core vulnerability" — her perceived lack of honesty and trustworthiness.

This might be the moment in which Hillary Clinton's serial prevarications actually begin to matter to most voters. It's not the cough. It's the cover-up.