I would say that this part from article 1, section 9: "The importation of negroes of the African race from any foreign country other than the slaveholding States or Territories of the United States of America, is hereby forbidden; and Congress is required to pass such laws as shall effectually prevent the same" actually protected the international slave trade rather than moved away from it.
Good point. They attempted to make the international slave trade legal. It just didn’t work, as the border never became effective.