According to the political parties should run on polarizing issues to mobilize their ideological base and force moderate voters to make stark choices or not vote at all

The word that comes in the blank space is; wedge issue theorem.
A wedge issue is a political or social issue, regularly of a questionable or disruptive nature, which parts separated a statistic or populace gathering. Wedge issues can be publicized or freely circulated trying to debilitate the solidarity of a population, with the objective of enticing polarized people to offer help to a rival or to pull back their help altogether out of disillusionment. The utilization of wedge issues offers ascend to wedge political issues. Wedge issues are also called hot button or third rail issues.