Nowhere in that article does it use GOP as a pronoun nor had it claimed it is used as one. I'm just thinking that the GOP are hypocritical enough to adopt it as one.
Definition of a Pronoun :
The word that is used in place of a noun or a noun phrase is known as pronoun. A pronoun is used in place of a noun to avoid the repetition of the noun.
GOP isn't a 'pronoun,' it's a nickname and has been for decades.
[sigh] A pronoun is a word you use instead of a proper name. "The Model T was built for decades. It was America's most popular car." In that sentence 'it' is a pronoun.
"The Model T was a common sight in every city and town. Everyone knew someone who drove a Tin Lizzie." Tin Lizzie was another name for the Model T. 'Tin Lizzie' isn't a pronoun, it's a proper name.
GOP isn't a 'pronoun' and never was. It's always been a proper name and that's how I used it. Like the word 'fish' it can mean a single member of the Republican Party, or the Party as a whole.