No, wasn't waxing philosophical. Rather thinking of the foundation of it all, economics, national defense, liberty, justice, social welfare. It pretty much all falls under those priorities, and deficiencies within any one of them are what tip the scales of priority. Don't view the center moving around as much as circumstances can dictate how far people are able to stray from it.
Economics - big shifts here. Trickle down was the huge, apparently fallacious, move back from the accepted
understanding that lasted through the mid 20th century by both parties to a position essentially from the 1920's.
National Defense - both parties are largely in alignment here, although the blunders at the beginning of the
millenium caused fringe members on both sides to question some of the military adventurism.
Liberty - both sides seem to be for it - unless it breaks with 'good behavior'. Whatever the ideological
fad of the party is as to what is 'good behavior' seems more of a distinguishing feature. Hard to draw
any solid lines here.
Justice - Until very recently, the nation as a whole bought into the idea of rule of law. Now, that has become
a partisan issue - the law should only apply to your political enemies. At least they still seem in agreement
at heart though - even if the degree may differ.
Social Welfare - here we do see a significant difference, at least in the post New Deal structure. True laissez faire
was gone already, but the question was where should the largess go. That struggle has largely been at the heart
of the differences. Prior to the New Deal, things were more muddled - as with most issues.