Plagiarism by Donald Trump Jr. ?

I assume it's because of mutual agreement by the parties involved. Speechwriters are usually happy to get paid, but I suppose they could donate their services as well.

I think using someones music (like Springsteen telling Christie to stop using his)

Doesn't politicians use other sources for their speech? I'm not sure where it can be wrong, but the perception can be negative to some people.

I wish more politicians would use, "Ask not what the country can do for you. Ask what you can do for the country."

They could ask that, but then those on the left side of the isle don't believe in those great words by JFK anymore.