I consider the difference between a system founded on the legislatures only, and one founded on the people, to be the true difference between a league or treaty and a constitution.
James Madison (1836). “The Debates in the Several State Conventions on the Adoption of the Federal Constitution: As Recommended by the General Convention at Philadelphia, in 1787. Together with the Journal of the Federal Convention, Luther Martin's Letter, Yate's Minutes, Congressional Opinions, Virginia and Kentucky Resolutions of '98-'99, and Other Illustrations of the Constitution”