Melania’s 2016 speech is 1377 words. Michelle’s 2008 speech is 2223. In the diagram you see three distinct diagonals which are the verbatim phrases copied. I am sure that someone with more interest in these things can apply some NLP knowledge and graph something better.
PS: I just noticed that both speeches close with the same phrase: “Thank you, God bless you, and God bless America” (the phrase is seen at the top right corner of the plot).