On Oct. 21, 1984, President Ronald Reagan was asked to give a summation as to why he should be re-elected at the end of his debate with Democratic challenger Walter Mondale. His meandering, unfocused response kicked off speculation that he was suffering from cognitive decline that only intensified in his second term. Here is part of it: “Several years ago, I was given an assignment to write a letter. It was to go into a time capsule and would be read in 100 years when that time capsule was opened. “I remember driving down the California coast one day. My...