Republican vs republican

Republican and republican both are nouns.

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

Republican (noun)	republican (noun)
a tributary of the Kansas River that flows from eastern Colorado eastward through Nebraska and Kansas	an advocate of a republic (usually in opposition to a monarchy)
a member of the Republican Party

Republican (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