I recall Obama being mocked in the early days of his presidency for relying heavily on a teleprompter, and I bet there are many who wish Trump would rely more on it.
A president must be mentally swamped 24/7 and have a dozen different things on his mind at any given moment. You cannot expect such a person to come up with spontaneous great historic and eloquent stuff on the spot to speak about Polish history when visiting Warsaw or Yale at a commencement or extensive minority facts and data from memory at the funeral of some civil-rights icon. Nobody has that brainpower. In fact, it’s a wonder that there’s anything a president doesn’t need a teleprompter for; there are a hundred different topics for a hundred different public settings.