Minority Rule

A fundamental aspect of republican (form, not party) governance is protection against what is colloquially dubbed "tyranny of the majority." A pure democracy allows 50%+1 members to impose their will on everyone else, whereas republics have structures that preclude majorities from, among other things, infringing on individuals' rights. Our republic also separates powers both horizontally (tripartite federal government, bicameral legislature) and vertically (many functions of government are reserved for the states, and many others occur at the local level).

Our republic's structure naturally creates (see Duverger's Law) a two-party outcome, with minor parties existing only on the fringe, as spoilers, and/or as incubators for novel policies and ideas. The major parties are evolutionary beasts, adjusting as the political and cultural landscapes adjust, and holding only a tenuous or nominal anchor to unmoving bedrock ideology. Thus, we can see phenomena such as working class voters, who were for decades considered the "base" of the Democratic party, losing that distinction to well-to-do urban college graduates.