What party was against the Louisiana Purchase?
The Louisiana Purchase was done by Thomas Jefferson who was a Democrat-Republican. The Federalist Party thus opposed the move.
Why was Jefferson willing to go against his ideas of strict construction to purchase the Louisiana Territory?
Federalists, despite being the party that supported a strong central government, opposed the Louisiana Purchase. It was opposed mostly because President Thomas Jefferson, a Democratic-Republican who supported a strict, or narrow, view of the Constitution, went against his principles of small government and bought the territory anyway. The Federalists used this as fuel against Jefferson and the other Democratic-Republicans in an era where party politics sharply divided the country.