Winnow
From dKosopedia
Winnow is a verb meaning to remove the undesirable from the desirable. The agricultural origins of the term reference the separation of the chaff from grain by means of a current of air. In political terms, winnowing refers to the administrative or electoral thinning of candidate pools. In the United States, the pool of presidential candidates is winnowed across the party presidential primary election and caucus season every four years as candidates fail to receive sufficient electoral support and delegates to continue their campaigns.