That sounds nice, but I think it's wrong. I don't know about other states, but most folks who were Democrats in the 1960's here in Georgia remained Democrats into old age and death. Presidential wise Georgia only went Republican in 1972 when Nixon won 49 states, in 1984 when Reagan won 49 states, then in 1996 to present. 1972 and 1984, Georgia went the same as the rest of the country with the Republican winning 49 states. So there's no difference there.
The most telling that most Democrats remained Democratic was Georgia didn't elect our first ever Republican Governor until 2002 along with our first ever republican state legislature. Georgia had elected only 4 Republican House of Representatives member from our inception until 1994. Newt Gingrich was the lone Republican congressman in 1994, all the rest were Democrats. As late as 2004, we still had two Democratic senators Max Cleland and Zell Miller.
The thing here, at least Georgia is the state remained loyal to the Democratic Party. I look on 2002 as the turning point when Republicans took over Georgia, although one could go back to 1996 the year we voted for Dole as president and our congressional delegation went from majority Democrat, 9 D's to 1 R to majority Republican 7 R's to 3 D's.
My point is at least in Georgia, those who were Democrats in the 1960's remained Democrats. There was no mass migration from Democratic to Republican in either the 1960's or the 1970's. The best possible reason for Georgia switching from Democratic to Republican in either 1996 or 2002 was the addition of new, younger voters to the rolls and the influx of folks who fled the north for the south.
For most of my life here, the winner of our elections was decided in the Democratic primary, not in the general election. The general election was just for show. That began to change in 1996 and finally the general election meant something real by 2002.
