Arlen Specter, a pugnacious and prominent former moderate in the U.S. Senate who developed the single-bullet theory in President John F. Kennedy’s assassination and played starring roles in U.S. Supreme Court confirmation hearings, lost a battle with non-Hodgkin lymphoma when Congress is more politically polarized than anyone serving there — or living in America — can remember.

Specter, 82, died Sunday after spending much of his career in the U.S. Senate warning of the dangers of political intolerance. President Barack Obama ordered U.S. flags at the White House and other public buildings flown at half-staff today, the day of Specter’s funeral.