their most formative coming of age years, most boomers used to be progressive.

Then something happened and the aging electorate has been filling the 50+ void left by the Greatest and Silent Generations dying off with more Republicans (up from 39% to 56% since 1996) than Democrats (up from 41% to only 50%).

From the article linked below:
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The U.S. electorate is aging: 52% of registered voters are ages 50 and older, up from 41% in 1996. This shift has occurred in both partisan coalitions. More than half of Republican and GOP-leaning voters (56%) are ages 50 and older, up from 39% in 1996. And among Democratic and Democratic-leaning voters, half are 50 and older, up from 41% in 1996.
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