This paper argues that among the most consequential institutional variables affecting how constitutional orders operate are two relating to political parties. The first is the nature of the political party system (multiparty, two party, dominant party), which influences the actual separation of powers regardless of the form of government enshrined in the constitution. The second is the method political parties use to choose their candidates for chief executive in a general election. This helps to determine how easy or difficult it is for an “outsider” candidate posing a risk to the values of constitutional democracy to capture a major party and smooth a path to power. And yet, despite the importance of political parties to the constitutional order in these and other ways, they are rarely viewed as proper subjects for constitutional design. Although perhaps understandable from a historical perspective, this is mostly mistaken from a contemporary functional one.