To add to my previous post I don't particularly see anything wrong with a speech writer taking from their own "greatest hits" or even misappropriating talking points from other speeches but I'd say it should be common sense that you don't take from the speeches you can expect to be compared and contrasted with.
In the time where people were posting that Trump Jr's speech had talking points taken closely from an American Conservative article and before it came out that the writer of the article was in fact one of the speech writers I looked at it and said "I really don't have a problem with a speech writer taking an analogy from somewhere and not crediting it, should they probably have reworded it a bit? Probably but meh I don't think it's a big deal."
I think the public's perception that every speech is an original composition is slowly changing but in the mean time there will be more of the overzealous plagiarism bot stories and the counter story "NAME gave identical speech TIME apart".