Consider how accurate it is to describe the USA as having a two-party system.

The United States of America is infamous for a lack of electoral success by third parties, such as the Libertarians and Greens. This is perhaps best explained by the first-past-the-post electoral systsem used in Congressional elections, and indeed the Presidential Election. Despite capturing 19% of the vote in 1992, Texan billionaire, Ross Perot, failed to win a single Electoral College vote. As a result of this, those holding more fringe views (e.g. democratic socialism or minarchism) subscribe to membership of the two major parties (Democrats/Republicans). This has resulted in the branding of these parties as 'umbrella' - containing a plethora of political views, both fiscal and social. Moreover, the inherently political nature of American culture means that the election cycle is constantly in an ongoing process, especially with elections to the House every two years. This requires enormous levels of campaign funding, best provided by the respected major parties. In terms of Presidential elections, the vast scale of America means that funding in the hundreds of millions is required to succeed. There is a direct correlation in US politics between victory and campaign finance.

Nonetheless, there has been evidential success of fringe parties in US politics: Two independent members of the Senate. Decentralisation of the major parties gives power to individual caucuses (consider the role of the Freedom Caucus and Tea Party in the role of the 2013 government shutdown) (Southern Republicans are more socially conservative than Maine Republicans, for example e.g. Ted Cruz and Susan Collins) - there is little in the way of uniformity. Electoral votes for third parties (1912 - Theodore Roosevelt and Progressives; 1924 - Follet and Progressives; 1948 - Strom Thurmond and Dixiecrats; 1968 - George Wallace and American Independents; 2016 - faithless electors for Sanders, Kasich, Powell, Faith Spotted Eagle).