Edward Casey O'Callaghan (born June 8, 1969) is an American attorney who served as the co-chief of the terrorism and national security unit of the U.S. Attorney's office for the Southern District of New York, who resigned in July 2008 to join John McCain's presidential campaign. One of three leaders of Sarah Palin's Alaska "truth squad," O'Callaghan became the public face of Palin's legal defense against ethics charges related to her former brother-in-law, the so-called "Troopergate." From 2009 to 2011, he worked at the law firm Nixon Peabody, then from 2011 to 2017 he was a partner at the New York office of law firm Clifford Chance. In 2017, he became the principal deputy assistant attorney general of the National Security Division at the U.S. Department of Justice.