Why is the Hillary Clinton campaign so very upset about the supposed "plagiarizing" by Barack Obama in his campaign speeches?

I don’t understand why the Clinton campaign sees Obama’s use of words or phrases as a detriment to him and his campaign. How many people, both privately and publicly, have used JFK’s words or MLK’s words? I simply don’t understand how Obama’s candidacy could suffer , or why it should suffer, for such an inconsequential reason.