A common misconception of impeachment is that it means his or her removal from office, when it actually functions as an indictment of a public official. Impeachment does not necessarily result in removal from office; it is only a legal statement of charges.
Porter is a dark style of beer developed in London from well-hopped beers made from brown malt. The name was first recorded in the 18th century, and is thought to come from its popularity with street and river porters.
I would put it this way: porter is the genus and always was. Stout was a sub-genus, meaning only, a strong variety of porter. The term brown stout probably predates that of porter pace the stout porter theory of origin. There was a pale stout as we all know.