Misjudge a moment or say the wrong thing and a US candidate can quickly find him or herself out of the race -- or at least on the wrong track.
But it's not just a slip of the tongue that can derail a campaign -- there are a number of other issues, peculiar to the US, that weigh on the minds of the American voter when they walk into the ballot box. That's not to say that politicians haven't tried to buck the trend. But this is where the wheels have started to come off.
Clinton, who returned to the campaign trail on Thursday, claimed
she "didn't think it was going to be that big of deal."
But that will do little to assuage voters in a country with a history of less than healthy commanders-in-chief.
"The ramifications of someone being in poor health and potentially dying mid-term are enormous," says Timothy Stanley, a US historian and columnist for CNN and Britain's Daily Telegraph.
"In the past, you had people like John McCain running for president, who was in his 70s when he did so. You had a controversial vice president -- Sarah Palin. George H. W. Bush had the same issue -- he had Dan Quayle."
The possibility that a president could die or require serious medical assistance while in office isn't as far-fetched as one may think. William Henry Harrison died of pneumonia a month after taking office in 1841. Woodrow Wilson suffered a massive stroke while in office in 1919, and his medical condition became a closely-guarded secret from the public, with his wife assuming affairs in his absence. Franklin D. Roosevelt died of a massive cerebral hemorrhage while still in office.
The issue of health may be more pertinent in America -- where the vice president assumes the top job in the event the president is incapacitated -- than in countries with other systems of government.
Case in point: Great Britain, which runs on a cabinet government system that places less importance on a leader than on her political party.
British Prime Minister Theresa May has diabetes, but this barely came up during the race to lead the UK government. And even if she did become ill, it wouldn't immediately impact her cabinet, which collectively oversees government legislation.
'Show us the money'
Another odd quirk of US presidential campaigns is the expectation that candidates should release their tax returns.
Clinton has released
her most recent federal tax return for 2015, in addition to those from previous years. Donald Trump hasn't, despite a recent Washington Post-ABC News poll finding that 64% of Americans think he should -- including 41% of registered Republicans.
Stanley says the reason US voters fixate on financial disclosure is two-fold: To ensure candidates do not carry any conflicts of interest, and to gain an insight into their character.
"That Barack Obama relies on royalties tells us he's intellectual, he's not obsessed with business, he's not looking out to make a fast buck," he says.
"That Hillary Clinton relies so much on her income from speeches implies this is a woman who really is a professional politician -- she makes money out of it. So there is a transparency issue. It's also an interesting way to gauge the character."
All US candidates must privately submit their full financial history to the Office for Government Ethics. But a candidate's failure to publicly disclose tax returns can plant seeds of doubt in voters' minds -- like it did when Walter Mondale's running mate refused to reveal her family's financial dealings in 1984.
"There was the famous case of Geraldine Ferraro, running as the Democratic vice president. There were issues with her husband," Stanley recalls. "Unfairly that created the impression she was covering something up."
The all-American dream
Only in America does the vetting for political office also extend so conspicuously to the politician's spouse.
"'First lady' is a made-up title. It means nothing legally or constitutionally ... It is a reflection of the celebrity nature of American politics and it's deeply unhealthy," says Stanley.
He believes that America's obsession with who will become the next "first family" speaks to a "desire to see a president who reflects older values of monogamy and fidelity."
And the average US voter is serious on this issue. Previously, entire campaigns in America have been derailed by infidelity.
John Edwards, the former senator from North Carolina, ran for the White House in 2008, and was even considered as a potential running mate
for Barack Obama's ticket. But details of an extra-marital affair -- including a child produced from the relationship and reports of a sex tape -- ended that presidential dream.
Gary Hart made several bids
for commander-in-chief in the '80s and very nearly made it. But a 1987 investigation by the Miami Herald had revealed an affair with a young campaign aide. The ensuing media speculation proved to be too much for the then-front-runner, who was never able to recover momentum and withdrew from the race in March the following year.
Overseas the perfect family ideal is less important. French President Francois Hollande faced a media firestorm in 2014
over allegations of an affair with an actress, and his relationship with long-time partner Valerie Trierweiler broke down. Hollande's personal life made headlines for months, but it hasn't unseated him from office.
That same year in India, Narendra Modi, who at the time was the then-favorite to become the country's next prime minister, was forced to disclose for the first time in his political career that he was, in fact, married.
Modi's family arranged the marriage
when he was in his late teens and the pair separated after three years but never divorced. It didn't stop him from declaring that his single status made him the perfect candidate
-- and although his opponents tried to use this information against him, Modi's coalition won handily on election day.
Back in the US, Clinton regularly campaigns with her husband Bill and daughter Chelsea by her side. Even thrice-married Trump understands US voters need to see a strong family unit, with his wife and children often joining him on the trail and at the national party convention last summer.
Want to crack open a beer?
American voters also want a president they can relate to. They want to see candidates interact with them on a personal level, to understand their struggles and -- perhaps most importantly -- to show a sense of humor. It's a regular occurrence to see politicians popping up on the American late-night circuit.
"They are a test on your ability to speak to ordinary people. It's very important to Americans that their president can make them laugh," says Stanley.
"You have to appear on Saturday Night Live... That tradition of appearing on it has been around since the '80s but it's really taken off in recent years. Palin went on it. McCain went on it. Obama went on it. Everyone gets on Saturday Night Live. You've got to be prepared to be laughed at and show that you get the joke."