I would say that the majority of people are registered to vote as a member of one party or another. But the independents (or unaffiliated) make up an important voting block. It's difficult, if not impossible, for someone to get elected president without a majority of independents along with their party-line vote. This is further complicated by the fact that independents don't fit into any particular political niches and their political views and philosophies are all over the political spectrum.

As an example, I have views that are more "conservative" than those of many Republicans, and also some that are more "liberal" than many Democrats. And I also have views that are not espoused by either party, and some that are commonly rejected by both parties. I don't think I'm all that unusual in this respect in relation to other people who self-identify as independents or unaffiliated.