Answer:
Ronald Reagan's age
Explanation:
Reagan was the oldest president to have ever served (he was by this point 73), and there were many questions about his capacity to endure the grueling demands of the presidency, particularly after Reagan's first debate with Mondale on October 7.
In the next debate on October 21, however, in response to a question about his age, Reagan joked, "I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience." Mondale himself laughed at the joke, and later admitted that Reagan had effectively neutralized the age issue.
