Listening to yet another round of Republican infighting raised anew the old questions of why one faction doesn't split from the other. I have my own answer to the question, which is that all sides covet the party organization's fundraising apparatus. But I suddenly found the old question begging a new one: why is it up to disaffected factions to leave the party or not?
The more I think about the American Bipolarchy, the more convinced I become that it is a structural rather than a conspiratorial phenomenon, the result of a sequence of decisions of policies, few of which were designed consciously to exclude rival parties. I wonder whether invoking the Bipolarchy creates a deceptive image of two powerful parties on the model of the monopoly parties of one-party states. The fact is, the Democratic and Republican parties lack a particular power that is characteristic of tyrannical parties elsewhere. When we think of the history of communist parties, for instance, we likely think of a succession of purges. These purges would not only eliminate people from positions of power within the parties, but often would expel them from the parties entirely, which in one-party states was tantamount to disfranchisement. Elderly purge victims like Vyacheslav Molotov might spend the rest of their long lives begging to be reinstated into the ruling party. Nothing like this happens in the dominant American parties.
Nobody gets thrown out of the Republican party for failing to toe the current ideological line, no matter how many people call for or dare dissidents to go elsewhere. All the groups can call each other "RINOs" or otherwise disparage each other's partisan credentials, but no one has the power to state as fact that someone else is no longer a Republican. On one hand, this looks like a matter of common sense; if one faction purged another, the losers would have nothing else to do but join the other major party or form a new party, and it makes no sense to force people to vote against you in the general election. On the other hand, it may have been a historical accident that revealed the genius of this reticence, since recent history, at least, has shown that dissidents, if not pushed out or purged, will not leave. This wasn't always the case a century ago. The more local you got, especially, primaries very often resulted in independent tickets as recently as 100 years ago. In my research on the city of Troy I found that the 1905 mayoral election was a four-way contest, not counting smaller parties like socialists or prohibitionists, because independents had split from both the Democratic and Republican parties. But this tendency seems to have become less pronounced as the 20th century went on. Perhaps there was an ultimate concession that splintering was always futile, but perhaps something else was happening that made dissidents less likely to bolt. What that might have been may be a key to the consolidation of the Bipolarchy, and that makes it a subject for further research.