If you go back to Kennedy vs. Nixon–it was even easier. Remember, despite looking relatively young and fit, JFK suffered from Addison’s Disease and had various health problems dating back to his childhood. According to a great biography I recently read (Jack by Geoffrey Perret), the affects were numerous, particularly to his lower back…which even periodically forced him to use crutches just to get around. The use of crutches was largely hidden from the press and those members who did see it didn’t see much reason to report it. Also according to Perret and verified by the History Channel, Kennedy was administered last rites at three times before his presidency.
In other words, given the microscopic media, social media and overall political climate today, there absolutely would not be a President Kennedy (or FDR) due to health concerns alone.
Back to the 21st century, it’s not just the candidates themselves, but their families under that microscope too. We saw this in 2008 when David Shuster — whom I would argue didn’t say this with any malicious intent — said that Hillary was “pimping out” Chelsea to appeal to women voters (he was suspended from MSNBC shortly thereafter). We saw it that same year with the treatment of Sarah Palin and Trig, her newborn son with Down’s Syndrome, when sites like The Daily Kos alleged the VP candidate faked the pregnancy to cover for her teenage daughter Bristol. And we saw it again in 2012, with the low-water mark being when Mitt Romney was actually accused of killing a woman by a pro-Obama super PAC.