Video proves Clinton suffering seizures? Not so, I was there

Two months later, that innocuous exchange has become the fodder for one of some Trump supporters' most popular conspiracy theories: her failing health.

Much of such speculation about the state of Clinton's health stems from a concussion she sustained in December 2012 after fainting, an episode her doctor has attributed to a stomach virus and dehydration.

Republican strategist Karl Rove later called it 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.

A July 2015 letter released by Clinton's campaign proclaimed her in "excellent physical condition and fit to serve as president of the United States," according to Dr. Lisa Bardack, an internist and chairman of the Department of Medicine at the Mount Kisco Medical Group in New York.

The conservative Fox News host Sean Hannity opened a 6-minute Thursday night segment titled "Hillary's Health" by saying, "as speculation swirls about Hillary Clinton's health," citing a headline from the right-wing news site Drudge Report.

Hannity repeatedly played the muffin shop footage, describing what Clinton was doing as "this sort of twitching thing that she does in front of reporters that was really bad" and then as "a violent, violent, repetitive jerking of the head."