What action did jefferson do that may have been unconstitutional

The correct answer is the Louisiana Purchase.

While the President has the power to negotiate treaties, Jefferson likely got quite a bit ahead of himself when the land was purchased before the consent of the United States Senate.

Furthermore, the Federalists believed that the acquisition of territory itself might be unconstitutional.

common sense was a pamphlet by thomas paine which advocated the independence of the thirteen colonies from great britain.