The way we talk and perform social behaviours for one another (our repertoire) is a mechanism for transmission of social approbation and disapprobation.
A cosmopolitan repertoire is open and facilitates other exchanges, including the development of democratic forms of governance and market exchanges that are mutually beneficial with few negative externalities.
A factional repertoire is closed, inward, and forecloses upon political and market exchanges.
Adam Smith was very concerned about factions, and so were many other early political economists.
And so am I.
I think Evangelicalism in the US is a large informally organized faction that affords approbation for actions that benefit those inside the faction but that don't benefit outsiders and sometimes harm outsiders. That faction is held together informally through the adoption of a peculiar repertoire that has a set of shibboleths to help identify outsiders. As a large informal group, Evangelicalism has sufficiently surrounded the median voter such that it can grant or withhold legitimacy from politicians.
A shibboleth is usually designed to identify outsiders and keep them out.
The idea that it is not really about what people believe is super important. Sincere Evangelicals who carefully think through what they believe hold on to a "true Evangelicalism" and mostly maintain a careful connection between belief and practice.
However, EINO's "Evangelical In Name Only" might claim to hold a belief but probably can't explain how that belief is systematically related to other beliefs or to practice.
The crucial point is when means and ends become disconnected, or when a means becomes an end in itself.
So, a flag is intended to help hold an army together, but devotion to a flag for itself is merely symbolic and loses its connection to real ends. Many Evangelical beliefs are like this, as are many beliefs of any religious or exclusionary group.
What we are observing is in part the struggle Evangelicalism has been going through in maintaining that position about the median voter.