Republican Party vs republican

Republican Party and republican both are nouns.

Word	Noun	Adjective	Verb	Adverb
Republican Party	Yes	No	No	No
republican	Yes	Yes	No	No

Republican Party (noun)	republican (noun)
the younger of two major political parties in the United States; GOP is an acronym for grand old party	an advocate of a republic (usually in opposition to a monarchy)

Republican Party (adjective)	republican (adjective)
	relating to or belonging to the Republican Party
	having the supreme power lying in the body of citizens entitled to vote for officers and representatives responsible to them or characteristic of such government