Regarding Jacoby’s claim that language in public discourse has become simplified and debased over time, see this story in the Washington Post published in the run up to the last presidential election: “‘Trump’s Grammar in Speeches ‘Just Below 6th Grade Level,’ Study Finds.”
If you’re really interested in this subject, here’s a whole book:
Lim, Elvin. T. 2008. The Anti-Intellectual Presidency: The Decline of Presidential Rhetoric from George Washington to George W. Bush. New York: Oxford University Press.