United States v. Carolene Products (1938) established a dichotomy between enumerated and unenumerated rights. Under Footnote Four, laws that infringed provisions of the Bill of Rights would be scrutinized closely. By contrast, all other sorts of rights, including liberties protected by the Due Process Clause, would be afforded only rational basis scrutiny. Williamson v. Lee Optical (1955) made that rational basis scrutiny even more deferential. That test became the New Deal settlement on the Due Process Clause. Until it wasn't.
Griswold v. Connecticut (1965) found that a right of privacy could be found in the "emanations" of the Bill of Rights. At least on paper, the Court was trying to stay within the Footnote Four framework, though I'm not sure anyone really believed it. But Griswold made a more important move. To respond to the charge of Lochnerism, Justice Douglas sought to distinguish the Court's past cases. West Coast Hotel was retconned as a repudiation of substantive due process only for economic rights. By contrast, substantive due process was still permissible personal rights cases. Decisions like Meyers v. Nebraska or Pierce v. Society of Sisters were reaffirmed acceptable as First Amendment decisions, even though both predate the modern incorporation doctrine.
Here is how Justice Douglas attempts to reconcile the doctrine:
