Complex sentence: Sasse was a student and teaching fellow at Yale University in New Haven, Connecticut, from August of 1998 to May of 2004, however, beginning in the fall of 2002, Sasse lived exclusively in Washington, DC, where he was writing and conducting research.
Split into simpler sentences: Sasse was a student and teaching fellow at Yale University in New Haven, Connecticut, from August of 1998 to May of 2004. Beginning in the fall of 2002, Sasse lived exclusively in Washington, DC, where he was writing and conducting research.