Why the Zell Miller transformation?

[Indy Texas]

The biggest difference between Conservative Southern Democrats and Liberal Northeastern Republicans was that the latter were far more willing to put their own differences with the party aside to do what the leadership wanted, while the former were more likely to raise an active fuss when they didn't get their way and either threaten to run as independents or simply defect to the GOP.

From the end of World War II, when the hardcore Gilded Age-style Republicans who were strongly anti-New Deal had either retired, died or been voted out of office, until the rise of the Reagan Coalition in the late 1970s, the three overarching themes that held the GOP together were:

(i) Being more strongly anti-communist than the Democrats, either in substance or in style/perception.
(ii) A desire for the New Deal, Great Society and other welfare state programs to be run "more efficiently" which could cover anything from modest Dewey/Rockefeller-style tinkering to flirting with wholesale privatization.
(iii) General distance from organized labor, for reasons ranging from a good government desire to avoid corrupt machine politics to a general desire to destroy any bargaining power for workers in order to enrich large corporations.

When push came to shove, all Republicans, from the left to the right, were willing to vote in ways that advanced these three planks.

By comparison, I can't think of a single issue in the post-New Deal era where the entire spectrum of Democrats were willing to present a unified front on anything. And when defections happened, it was inevitably a case of a conservative (usually Southern) Democrat siding with the Republicans on a given issue.