In order to make the louisiana purchase, what justification did the government use?

President Jefferson endorsed the purchase but believed that the Constitution did not provide the national government with the authority to make land acquisitions. He pondered whether a constitutional amendment might be needed to legalize the purchase. After consultations Jefferson concluded that the president's authority to make treaties could be used to justify the agreement. Therefore, the Louisiana Purchase was designated a treaty and submitted to the Senate for ratification. The Senate ratified the treaty October 20, 1803, and the United States took possession of the territory December 20, 1803.

Political forces often influence public opinion.