To give you a sense of how party discipline works in some other democratic systems, at the party conference for the Conservatives currently taking place in the UK, the party’s leader, the Kemi Badenoch, announced that the Conservatives would commit to leaving the European Convention on Human Rights and repealing the Human Rights Act, enacted in 1997 under Tony Blair. The party believes these instruments have made it too difficult for the UK to address issues concerning asylum, immigration, deportation and the like. The decision to leave the ECHR was made in discussions among party leaders.

The point I want to flag is that the party has made this policy decision a part of the party manifesto, or party platform. Moreover, Badenoch has announced that the party will only permit candidates to run under its label if they support this commitment. People who oppose this commitment can remain party members, but they can’t run as a Conservative. Because the UK, like many democracies, does not have primary elections, the party’s leaders choose their nominees. Thus, the party can enforce its new commitment to leave the ECHR by controlling who runs under the party label in general elections. This is a powerful tool for party discipline that does not exist in the US (there are a few exceptional cases in which parties have legally succeeded in keeping candidates off the primary ballot for being too antithetical to the party’s policies, but these are exceptional cases in the US context).