Go to the 1 hour point in the video where Bernstein is discussing Tristan und Isolde by Wagner. To me this seems like blatant plagiarism on Wagner's part. He obviously knew the music to Berlioz's Romeo et Juliette, and this doesn't seem like a case of a Clementi piano concerto coincidentally containing the same notes as the intro to to The Magic Flute. Bernstein demonstrates that Wagner lifted entire motifs and IDEAS from a work about two star crossed lovers for HIS star crossed lovers.
Would you consider this a case of musical plagiarism? If not, what WOULD consist of musical plagiarism?