Wiki says Rosenstein is a Republican. He has been appointed to various government positions by both Dim and Republican presidents. He is a long term swamp creature who has worked for multiple administrations.
I agree he's been a disastrous appointment, but he is not a hard core Dim. He mostly seems like a guy who panicked and appointed a special counsel mostly to take the heat off himself.
Wrong, Rosenstein claims no Political Party, but worked under Obama eight years. Yeah, a Republican appointed Mueller. Yeah-right.