Calhoun's "Exposition" was completed late in 1828. He argued that the tariff of 1828 was unconstitutional because it favored manufacturing over commerce and agriculture. He believed the tariff power could be used only to generate revenue, not to provide protection from foreign competition for American industries, and that the people of a state or several states, acting in a democratically elected convention, had the power to veto any act of the federal government that violated the Constitution. This veto, the core of the doctrine of nullification, was explained by Calhoun in the Exposition: