The term chauvinism can cover it
smug irrational belief in the superiority of one's own race, party, sex, etc.
However, the term is not limited to views about political allegiances. To be explicit, you would have to preface it with a delimiting term, such as ideological chauvinism.
Also consider partisan
A strong supporter of a party, cause, or person.
This does not necessarily mean the adherent is blindly prejudiced against different points of view, but the usual connotation is one of a narrow-minded devotion to a cause.
A more colloquial term is drumbeater
One that supports a cause, especially vehemently.