Older people tend to be more likely to catch illnesses. Hillary Clinton and Donald Trump are the oldest presidential nominees ever to run against each other.
So what happens if one of them doesn't make it to election day? It's never happened before, but Clinton's exit from the 9/11 memorial early on Sunday is stirring up rumors about her health once again.
The members of the Republican National Committee and Democratic National Committee have the power to vote on a new nominee. The RNC's rules even allow for a whole new convention.
Here's a fact for you: President William Henry Harrison was the same age as Clinton is now when he died from pneumonia just 32 days after taking office in 1871.
Clinton says she'll be releasing more health records soon, and Trump is promising the same.