what principle of the constitution allows congress to override a presidential veto
Veto If the Congress overrides the veto by a two-thirds vote in each house, it becomes law without the President's signature. Otherwise, the bill fails to become law unless it is presented to the President again and the President chooses to sign it.[12] Historically, the Congress overrides the Presidential veto 7% of the time.[13]
Article One of the United States Constitution The Necessary and Proper Clause, as well as the Commerce and General Welfare Clauses have been interpreted so broadly that to this day, the Federal Government of the United States exercises many powers that are not expressly delegated by the States in the Federal Government by the Constitution, like the different social programs of the American Welfare State. However, James Madison, who wrote much of the Constitution, disagreed that Congress exercises powers that are not expressly granted in the Constitution; Madison, when he held the Office of President of the United States, exercised his Veto power against the Federal Public Works Bill of 1817, calling it Unconstitutional, since to him, the Federal Government does not have the power to build infrastructure.