Answer:
Stereotype
Step-by-step explanation:
A stereotype is a pre-established conception about an object/person/condition/situation, that is not factual or accurate since it is a perception that is mainly based on our limited point of view -whether promoted by society or not- and ignores other factors.
Gerald's belief about Republicans is an example of a stereotype because he, without knowing all the Republicans of the world, asserts that all Republicans are narrowminded, and thus, he will tend to discard any Republican's opinion.