The assassination this morning on Iranian soil of the political head of Hamas, Ismail Haniyeh, reminds us of the line Michael Corleone utters in “The Godfather” — “Barzini is dead. So is Phillip Tattaglia. Moe Greene. Stracci. Cuneo. Today I settled all family business.” We don’t intend any inapt parallels. Nor do we mean to make light of the war of retaliation that Iran is now threatening. We do want to suggest that what happened today is a moment to mark.