Which event significantly contributed to the decline of the Federalist Party?

The duel between Alexander Hamilton and Aaron Burr indeed marked a significant moment in the decline of the Federalist Party. Hamilton, a leading figure of the Federalist Party, was influential in shaping the party's ideology and policies. His death in the duel had a profound impact on the Federalist Party, leading to a loss of leadership and direction. This event symbolized the internal strife and division within the Federalists, contributing to their waning influence in U.S. politics during the early 19th century.

Other options provide context but do not directly tie as significantly to the Federalist Party's decline. The adoption of the Bill of Rights was a response to Anti-Federalist concerns, reflecting the party's struggle but not a direct cause of their decline. The election of Thomas Jefferson is often seen as a critical turning point, but it was the culmination of various factors including discontent with Federalist policies that led to their loss of power. The repeal of the Alien and Sedition Acts occurred later and was a popular action that further alienated the Federalists but was not in itself the initiating event for their decline. Thus, the duel is recognized as a turning point in Federalist fortunes, leading to diminished support and influence.