This Essay reexamines the question whether the Constitution empowered Congress to ban slavery in the territories. We explore that question by tracking two proposed additions to the Constitution, one that would empower Congress to ban the migration and importation of enslaved persons to all new states and territories and one that would oblige Congress to admit new states on an equal footing with the old. We show that the Federalists supported and the Convention adopted the migration provision, enabling Congress to restrict slavery to the states “now existing.” But the Federalists opposed and the Convention rejected the equal footing doctrine.

Over time, things changed. In debates over the admission of Missouri to the Union as a slave state, Southerners offered a popular, if implausible, reinterpretation of the “Now Existing Caveat” to the Migration and Importation Provision that rendered it practically irrelevant to the expansion
of slavery. What is more, Southerners pressed to extend a judge-made equal footing doctrine, urging that new states were entitled to legalize the ownership of people just as the old states were. Chief Justice Roger Taney wrote the Southern interpretation into the Constitution in the Dred Scott v.
Sandford opinion, ignoring the Now Existing Caveat and embracing the equal footing doctrine as a matter of constitutional compulsion. While Dred Scott has not survived, the equal footing doctrine now undergirds the idea of equal state sovereignty in such U.S. Supreme Court decisions as Shelby County v. Holder. Meanwhile, the Federalist constitutional settlement has all but disappeared from view.