This is from an article in the New Yorker that I have been reading.
The principal shortcut that people use in deciding which candidates to vote for is, of course, the political party. The party is the ultimate Uncle Charlie in American politics. Even élite voters use it when they are confronted, in the voting booth, with candidates whose names they have never seen before. There is nothing in the Constitution requiring candidates to be listed on the ballot with their party affiliations, and, if you think about it, the custom of doing so is vaguely undemocratic. It makes elections a monopoly of the major parties, by giving their candidates an enormous advantage—the advantage of an endorsement right there on the ballot—over everyone else who runs. It is easy to imagine a constitutional challenge to the practice of identifying candidates by party, but it is also easy to imagine how wild the effects would be if voters were confronted by a simple list of names with no identifying tags. Every election would be like an election for student-body president: pure name recognition.