Final answer:
Jimmy Carter, Bill Clinton, Barack Obama, and Joe Biden were the Democratic candidates who successfully won the presidency since 1968.
Step-by-step explanation:
The Democratic candidates who successfully won the presidency since 1968 were:
- Jimmy Carter (1976)
- Bill Clinton (1992, 1996)
- Barack Obama (2008, 2012)
- Joe Biden (2020)
These Democratic candidates secured the presidency in their respective election years. The years mentioned represent the election years, and the inauguration for each president took place in the subsequent January.