Do the math(s)
Millennials are more likely to vote Clinton:
https://www.statista.com/statistics/540686/choice-of-millennials-between-electing-trump-or-clinton-in-2016-us-presidential-election/
Millennials are more likely to use Facebook:
https://www.statista.com/statistics/187041/us-user-age-distribution-on-facebook/
Couple with that the fact that the button could be rolled out geographically in certain states...
(Disclaimer: I am no more than interested observer and have no voting rights in the US election.)
Biting the hand that feeds IT
