Not a gaffe. In writing, we use quotation marks to show when a quoted passage starts and ends, and some people mimic this orally by using the words "And I quote"...."End of quote". The tweet omitted the first introductory phrase, so "end of quote" sounds out of place.
He said "Let me repeat the line", similar to "Let me repeat that" or "Let me say that again."
I don't know why the tweet didn't show the actually embarrassing gaffe, which was when he said "presidency" in place in "pregnancy".