Why do the authors argue that the limited two-party system in the US is prescriptive rather than descriptive?

The authors argue that the limited two-party system in the U.S. is prescriptive because it shapes political behavior and party alignment rather than merely reflecting existing preferences among the electorate. By establishing rules, such as winner-takes-all electoral systems and ballot access laws, the system encourages voters to align with the two dominant parties, thereby marginalizing third parties and alternative viewpoints. This prescriptive nature reinforces a binary choice, limiting the diversity of political expression and shaping public discourse in a way that privileges the established parties.