An interesting and worthwhile article.

Many years ago, I made a similar point to a friend of mine: that the U.S. Rep. Party attracts a relatively cohesive group of people, while the Dem. Party is attractive to various people who have little in common. He replied that there is a strong commonality among Dem. supporters: the idea that government is an effective and beneficial way to deal with societal problems.

I've thought about this a lot since, and have not really come to any conclusions. However I will say that it seems possible that, while groups trending Democratic are not very cohesive when measured on some scales (e.g., social & economic permissive/restrictive scales, as in this article), they are relatively cohesive when measured on other scales.