Byrd sought the Democratic nomination in a special election in 1966 for the balance of his father's sixth term. He faced a strong primary challenge from a longtime opponent of Massive Resistance, fellow state senator Armistead Boothe of Alexandria, fending it off by 8,225 votes–a margin of less than a percentage point. On the same day, two of his father's longtime allies, Senator A. Willis Robertson and Congressman Howard W. Smith, were toppled by more liberal primary challengers. Although Harry Jr. easily won the general election in November, the 1966 primaries marked the beginning of the end for the Byrd Organization's three-decade dominance of Virginia politics.