Earlier quoted context omitted.
While RFK sometimes got help from Edwin Guthman and Peter Edelman, he also spoke extemporaneously sometimes, most famously when he had to announce the death of Martin Luther King to a crowd that hadn't yet heard the news: https://kennedykingindy.org/full-rfk-speech
Where are the politicians today who can quote Aeschylus at will? What happened to our national discourse that we’ve filled it with dimwits?
Mitt Romney wasn't bad.
If you mean specifically quoting Greek poets and philosophers I would imagine Obama could (and has in speeches) but hard to tell which he wrote himself of course.