New
studies at Northwestern University show that when a minority person is reminded of their membership in that minority, they are less likely to prefer a minority candidate than when they are reminded of their exclusion from the majority.
Among students who were asked to write about being Asian (the "affirmational condition"), 26% expressed a preference for Obama, 68% preferred Clinton, and one was uncommitted; among subjects who were asked to write about being not Caucasian (the "negational condition") the results were totally reversed -- 63% for Obama, 26% for Clinton, and two uncommitted.
When a similar experiment was carried out among 38 Latino students at UCLA, it yielded similar results. Among students who were asked to write about being Latino, 26% preferred Obama, 58% preferred Clinton, and three were uncommitted; among those who wrote about not being Caucasian, 58% preferred Obama and 37% Clinton while one was uncommitted.
Dedicated Republicans and Democrats aren't going to be swayed by membership or exclusion, but it's vital that both parties portray themselves as a group an uncommitted voter would want to join. For instance, both say they're composed of "the people"; while (generally speaking) Democrats would like you to think that all Republicans are ultrarich and Republicans would like you to think that all Democrats are elitist, it may be more important for each party to say what they aren't rather than what they are.