Political parties are vital to the operation of any democracy. Early U.S. political parties were formed by national elites who disagreed over how to divide power between the national and state governments. The system we have today, divided between Republicans and Democrats, had consolidated by 1860. A number of minor parties have attempted to challenge the status quo, but they have largely failed to gain traction despite having an occasional impact on the national political scene.
Electoral rules, such as the use of plurality voting, have helped turn the United States into a two-party system dominated by the Republicans and the Democrats. Several minor parties have attempted to challenge the status quo, but usually they have only been spoilers that served to divide party coalitions. But this doesn’t mean the party system has always been stable; party coalitions have shifted several times in the past two hundred years.
Political parties exist primarily as a means to help candidates get elected. The United States thus has a relatively loose system of party identification and a bottom-up approach to party organization structure built around elections. Lower levels, such as the precinct or county, take on the primary responsibility for voter registration and mobilization, whereas the higher state and national levels are responsible for electing major candidates and shaping party ideology. The party in government is responsible for implementing the policies on which its candidates run, but elected officials also worry about winning reelection.
A divided government makes it difficult for elected officials to achieve their policy goals. This problem has gotten worse as U.S. political parties have become increasingly polarized over the past several decades. They are both more likely to fight with each other and more internally divided than just a few decades ago. Some possible causes include sorting and improved gerrymandering, although neither alone offers a completely satisfactory explanation. But whatever the cause, polarization is having negative short-term consequences on American politics.