The political party history in the united states is fraught with the two primary parties stating negative things about the other. specifically, member of both parties have stated that the other party is not in the best interest of america (both parties have used terms such as zealot, thug, hack, elitist, radical, extremist). this process is referred to as:

This process is referred to as: Boundary heightening

Explanation:

What does Boundary heightening mean?

This is a stress factor in which the majority group members strive to show their affability through exaggeration of their similarities or their differences so that they can associate with group members. Individuals keep being told how different they are using indirect ways such as through jokes, social exclusion ,etc. The individuals who are being isolated have not choice but to stay away from the counterparts or try to demonstrate those qualities that are needed to fit in .

in the above text we can see the use of words such as "extremist" radical"thug" which are exaggerated in characterising the differences that exist between the republicans and democrats , when they do this exaggeration the aim is to show how great the other one is as compared to the other ;this is boundary heightening

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

well to answer ur question to be completly honest