This makes the common and terrible assumption that humans don't change as they age. The fact that Millennials seem more to the left of Boomers is presumed to me

This makes the common and terrible assumption that humans don't change as they age. The fact that Millennials seem more to the left of Boomers is presumed to mean that the country will move left as the Boomers die. We must remember that the Boomers were those 1960s leftist radicals. Some day, decades from now, the Millennials will be elderly and conservative. Another bad assumption is that party platforms don't change, and that the current alliances will be forever unchanged.