why did some US politicians believe that the Louisiana purchase went against the US Constitution. #1 the president needed the Senate's approval before entering into treaties with foreign countries. #2 the Constitution clearly forbade the addition of new territories to the United States. #3 the cost of the Louisiana purchase was higher than allowed by the Constitution. #4 the Constitution required treaties with foreign countries to be approved by a national.. plsss help I will rate you a 5 !!!