I will need to reread this article by Dante Chinni and Stephanie Stamm at the Wall Street Journal a couple of times. I think the interpretation of the data is almost the opposite of what the article claims to show.
As you can see from the graphic above, the American electorate’s voting has become very slightly more Republican (margin of error) over the last 50 year and considerably less Democratic. The article purports to demonstrate that the degree to which Baby Boomers have become more Republican is offset by the degree to which Millennials and Gen Z is Democratic. I think it actually shows that a) the Silent Generation has changed a lot; b) the Baby Boomers have changed a little; and c) Millennials and Gen Zers are quite a bit more Republican than the Baby Boomers were at their age.
More research needed.
Considering how much the parties have realigned and sorted since the mid-1970s, I don’t think this chart tells us much.