In reference to 19th century presidents, Lincoln, of course comes to mind. No formal education but a man who considered his words and syntax in public speech before he spoke. Even in his recorded private speech he could make his sentences coherent (perhaps these are romanticized remembrances, I don’t know.)
19th century oratory was a very different thing than oratory today. But Lincoln was not a typical orator of his day. For one thing, the two speeches which are best known, the Second Inaugural and the Gettysburg Address are very short by 19th century standards. (The Gettysburg Address is short by today’s standards.) Of course, they may be best remembered precisely because they are short, and more like 20th century oratory than 19th.
And today’s American oratory owes a lot to the tradition of preaching, especially African-American preaching. Martin Luther King, Jr. is probably more responsible than anyone else for bringing this style to mainstream (i.e., white) Americans. You can hear the homiletic cadences in almost every good speech that is delivered today. Obama is a master of it, but you hear it in white politicians too.
I’m speaking here of prepared, scripted speeches. Off-the-cuff oratory in the 19th century, vocabulary aside, was probably not that much different than today. (Although we can’t know for sure, as all we have are later remembrances, which we can be sure are not accurate representations of exactly what was said.)
a man who considered his words and syntax in public speech before he spoke
Most politicians who rise to national prominence do this. Trump is the exception. That is the problem; presidents have to carefully consider their words.
And we haven’t touched on tweeting. Trump is a master of the tweet. He is really good at it. Whether or not Twitter is an appropriate medium for the President of the United States to communicate major policy announcements in and whether or not the subjects Trump tweets about are appropriate for the president to engage with, however, are different questions.