Final answer:
The December 1814 Hartford Convention resulted in the weakening and eventual downfall of the Federalist Party, due to public perception of their actions as unpatriotic during the War of 1812.
Step-by-step explanation:
The consequence of the December 1814 Hartford Convention was the weakening of the Federalist Party. The convention was a meeting of Federalist delegates from New England, where they discussed their grievances against the War of 1812 and the possibility of secession from the Union. This initiative took place while the country was still involved in the war, and the eventual revelation of their discussions, combined with news of American victories like Andrew Jackson's in New Orleans, led to widespread public condemnation of the Federalists. Perceived as unpatriotic, the Federalist Party lost the trust and confidence of the American people, which ultimately led to its decline and disappearance from the political scene.