The political scientist Eitan Hersh described these changes in a 2013 article. By matching the names of the victims’ families and neighbors to administrative records, he showed that they became more likely to vote in general elections after 2001, relative to similar people who were not relatives or neighbors of a victim. Family members became two to four points more likely to vote and neighbors two points more likely to vote. Remarkably, this was true in nearly every election between 2002 and 2012. The effect did not fade away. This graphic shows how family members became more likely to turn out:

Family members were also more likely to engage in other kinds of political activism: making donations to candidates and voting in primary elections. Neighbors also became more likely to vote in primary elections.

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This political activism had implications for the two political parties. Hersh traces changes in party registration and finds that, after the attacks, victims’ family members who were not registered Republicans became three points more likely to register as Republicans, compared with similar people who were not relatives or neighbors of victims. There was a similar, though smaller, shift in the party registration of neighbors.

Clearly, the terrorist attacks of 9/11 influenced our politics in many ways and for many years. They continue to do so today. Hersh’s research shows that those effects were distinctive — and durable — for the families and neighbors of the victims.