More on the Mark Stenner copying matter in Boca Raton
There is an issue here, although copying in speeches may draw less scrutiny than copying in academic papers and theses. Abraham Lincoln did not cite the Gospels in his "House Divided" speech, though much of his audience may have understood from where that text originated. It is less likely that Stenner's audiences were familiar with the work of Marc Lewis or David McCullough Jr.
As to the text --Students caught plagiarizing in class usually don't get credit for assignments; in college it can lead to suspension or expulsion. --, when Joe Biden was caught plagiarizing in his first year law class at Syracuse, he got an F and had to re-take the course. But he was not expelled, and he graduated and became a Senator and Vice-President.
Of relevance to academia:
Plagiarism in academic contexts: a look at the past