In Roemer's model, all political parties are assumed to consist of three types of factions—opportunists, militants, and reformers.
Opportunists seek solely to maximize the party's vote share in an election; militants seek to announce (and implement) the preferred policy of the average party member; and reformers have an objective function that is a convex combination of the objective functions of the opportunists and militants.
It has been shown that the existence of reformers has no effect on what policies the party announces.
Such unanimity to deviate can be rare, and thus PUNEs are more likely to exist than regular Nash equilibria.
(A nontrivial PUNE is one in which no party offers the ideal policy of either its militants or opportunists.)