national leader vs politician

national leader and politician both are nouns.

Word	Noun	Adjective	Verb	Adverb
national leader	Yes	No	No	No
politician	Yes	No	No	No

As nouns, politician is a hypernym of national leader; that is, politician is a word with a broader meaning than national leader:

national leader: a person who is a respected leader in national or international affairs
politician: a person active in party politics

Other hypernyms of national leader include pol, political leader, politico.

national leader (noun)	politician (noun)
a person who is a respected leader in national or international affairs	a person active in party politics
	a leader engaged in civil administration
	a schemer who tries to gain advantage in an organization in sly or underhanded ways