NYC was always a big Democratic stronghold. And the cities where the supposed inversion occurred did have a huge shift in population demographics.
The GOP did not shift left in a big way until TR and “progressive” politics. The Democrats were left-wing long before that; it’s in their published views even from the nineteenth century, reflected particularly where then Princeton University student Woodrow Wilson said that “socialism and democracy” were “one and the same” and compared it even to Bismarckian state socialism (which spawned national socialism and the European Union’s social market economy).
Don’t forget that the fifteenth goal of the communists was to “(c)apture one or both of the political parties in the United States”.
And where is "Princeton" located again?
Liberal socialists tend to come from liberal socialist areas of the country.