In response to Paul Krugman’s post from the other day, I don’t find it so strange that Democrats are a coalition of interests, Republicans are a unity of ideology. I find it very nearly inevitable.
First: the underlying and ongoing issue in two party politics in a capitalist representative democracy is always the haves versus the havenots. Democracy is a 1-person-1-vote principle and force for equality that automatically has a taste for downward income redistribution. Capitalism is a 1-dollar-1-vote principle and force for inequality that automatically has a taste for upward income redistribution. (They don’t put it this way, but a version of this principle is actually standard in median voter models, which are the leading models in rational choice political economy.)
Second, there are far more havenots than haves. Therefore the party of the haves is always, always focused on splitting the party of the havenots. Hence it constantly creates new ideologies for that purpose. Some of these ideologies must be based on on scapegoating and hate, since the goal is splitting the coalition of the havenots. The rest must be based on justifying inequality while pretending not to.
Third, the party of the haves succeeds only when it persuades some havenots against their own interests. Doing this largely depends on appealing to a taste for authoritarianism. Authoritarians accept false ideologies because they are told to by their leaders. Also, authoritarians are comfortable with antiegalitarian ideologies.
Fourth, as a matter of efficiency and effectiveness, all leaders of the party of the haves need to be on the same ideological page. Unity is far more important than specific choice of ideology. As long as leaders are unified, authoritarian followers quickly adjust to shifts in the party line. (And they will fall in line behind Trump.)
Fifth, the party of the haves is organized around real interests, not mystification. Therefore it naturally consists in a coalition of interest groups.
The reason that conventional rational choice political scientists think the two parties should be symmetrical is that they leave ideology and mystification, which is seen as “irrational,” out of their models.