A word to describe "political buyer's remorse"
Solution 1:
Voter's remorse would seem to be a straightforward parallel, and has a fair amount of usage.
The political equivalent of buyer's remorse is voter's remorse. --The Atlantic 2007-04 http://www.theatlantic.com/magazine/archive/2007/04/voters-remorse/305859/
Voters’ Remorse: Brits Regret Vote To Leave EU, Claim They Didn’t Know Their Votes Would Count; Millennials Especially Upset By Brexit Vote --Inquisitor headline 2016-06-25 http://www.inquisitr.com/3242585/voters-remorse-brits-regret-vote-to-leave-eu-claim-they-didnt-know-their-votes-would-count-millennials-especially-upset-by-brexit-vote/