Democratic presidential nominee Hillary Clinton fell ill Sunday in New York at a memorial service marking the 15th anniversary of the Sept. 11, 2001, terrorist attacks, leading her campaign to acknowledge she had been diagnosed with pneumonia two days earlier and bringing new attention to her health in the campaign.

Dave Robertson, chair of the Department of Political Science at the University of Missouri–St. Louis, appeared on the Charlie Brennan Show Monday morning on KMOX (1120 AM), discussing potential implications for the November election and also providing some history on issues of health in presidential elections.

Dave Robertson (Photo by August Jennewein)

“It’s going to be clear that they’re going to have to prove to the public and to the press that Hillary Clinton has a clean bill of health,” Robertson said when speaking to co-hosts John Hancock and Michael Kelley. “They’re going to have to go a little further than they probably wanted to in asserting that case. But the problem for her opponents is if they push too hard, that could backfire on them.”

It was suggested that Republican nominee Donald Trump could face similar pressure to be more open about his finances by releasing his tax returns.

“Most candidates have released those tax returns in the past, and Trump is kind of an exception on that,” Robertson said. “We’ll have to see if he can withstand the pressure that certainly is going to mount on him to release those records because people would like to know if he’s as wealthy as he says he is.”

As for whether either issue could alter the outcome of the election, Robertson didn’t rule out the possibility.

“It can be an issue for maybe 1 percent of the voters, 2 percent of the voters, and in an election like this one where so many people are undecided, it could sway a few people one way or another that could make a difference in the election,” he said.

Robertson wondered how disclosure of a health condition might have altered the outcome of the election in 1960.

President John F. Kennedy had denied that he had Addison’s disease – a disorder that occurs when the body produces insufficient amounts of certain hormones produced by the adrenal glands – when Lyndon Johnson raised the possibility that year.

But Kennedy did suffer from the disease, whose symptoms include fatigue, difficulty standing, muscle weakness, fever, weight loss, anxiety, nausea, headaches and changes in mood or personality.

“If people had known about Kennedy’s Addison’s disease in 1960 – an election that was incredibly close – Richard Nixon could have won the presidency,” Robertson said.

Kennedy was not the first candidate in the 20th century to face questions about his health in the lead-up to an election.

“The other candidate who was running for election – or re-election – was Franklin Roosevelt, who was seen as very ill in 1944 and, in fact, died three months after he took the oath of office again,” Robertson said. “So this is not unusual. There are lots of hidden health conditions that we become aware of later.”