Welcome to the Trump-Clinton conspiracy election
Pushing back, Clinton warns of murky ties between Trump and the Russian government, insinuating that her Republican opponent may be a puppet of Russian President Vladimir Putin.
Trump, a businessman and reality TV star, has frequently tossed out rumors about Clinton's health and sleep schedule on the stump and on Twitter, aiming to discredit her fitness for office.
Sensing an opportunity, Clinton's team seized upon the rumor-mongering after the GOP nominee plucked Steve Bannon, the executive chairman of the conservative website Breitbart News, to be his new campaign chairman this month.
Much of the speculation stems from a concussion Clinton sustained in December 2012 after fainting in her final weeks as secretary of state, an episode her doctor has attributed to a stomach virus and dehydration.
Republican strategist Karl Rove later cast the incident as a "serious health episode" that would be an issue if Clinton ran for president, fueling a theory the concussion posed a graver threat to her abilities than Clinton and her team let on.
When the accusations made their way into a recent Trump foreign policy address, in which he said she "lacks the mental and physical stamina" to fight Islamic State militants, Clinton's campaign felt they had to respond.
In the aftermath of hacked Democratic emails, Trump encouraged hackers from Russia to find Clinton's missing State Department emails, an apparent invitation for a foreign power to intervene in a U.S. election.