Ideology remains one of the most difficult concepts in the study of political parties. We have a general sense that ideology is a way of sorting out "what goes with what." That way, people who want lower corporate taxes also tend to want more restrictions on abortions and fewer restrictions on handgun purchases, even though those three issues have essentially nothing to do with each other. But who decides what goes with what?
Hans Noel has come closer than anyone to answering this question. Be sure to check out this nice profile from Matt Yglesias of some of Hans' recent research, which looks at the role that pundits have played in organizing American ideologies since the 1850s. Hans finds evidence that public intellectuals basically built ideologies regarding slavery in the 1850s, civil rights in the 1960s, and abortion in the 1980s and constructed the debating spaces that the parties would occupy in the following years.