the meaning of "get under his very thin skin"

[chance22]

I saw a video of Hillary making a speech in 2016, in which she said "It's not hard to imagine Donald Trump leading us into a war just because somebody got under his very thin skin."
I don't quite understand the second half of the sentence. Does the word "somebody" here refer to Hillary herself?
Would you possibly explain it?

 

[jutfrank]

I'm sure she doesn't mean herself. She's talking about a real war, with a different country.