Answer:
A. The president needed the Senate's approval before entering into treaties with foreign countries
Step-by-step explanation:
Why did some US politicians believe that the Louisiana Purchase went against the US Constitution?There was no provision in the Constitution about acquiring land from a foreign nation,President Thomas Jefferson took the advantage of this opportunity to justified the Louisiana Purchase by using his executive power to negotiate treaties with foreign nations.
The constitutional issue that was involved in the Louisiana Purchase making it illegal was because the constitution said nothing about acquiring new territory which lead to some prominent individuals to be against it believing he overstepped his Constitutional authority as president in buying the land but Congress ratified the Louisiana Purchase so it was constitutional.