This paper empirically examines whether the act of deciding to support a political party
can impact partisan leanings years later. We use the discontinuity in the probability of being
registered to vote around the 18th birthday to look at the impact of registration after the 9/11/01
attacks on party of registration. We …rst show that 9/11 increased Republican registration by
approximately 2%. Surprisingly, these di¤erences in registration patterns fully persist over the