He's '(as) stubborn as a mule'. [=he's very/extremely stubborn]
She 'has a stubborn streak'. [=she is often stubborn]
She's wrong, but she's too 'stubborn' to admit it.
(..) at your discretion, Mr. President. It might be good for you to have some support. Her presence undermines my authority as Secretary of State. Cathy, Petrov is incredibly stubborn. Trust me, I know. Why wouldn't you wanna have every asset available to you? - Allow me to do this, Mr. President. (..)2016 TvShow: House of Cards Title: Chapter 45 Season: 4 Episode 6