Palko may have been a last hurrah for the application of the doctrine of substantive due process in defense of citizens' basic rights at the state level. By reiterating the applicability of the Due Process clause of the Fourteenth Amendment to "fundamental rights", Palko is seen as paving the way for the later doctrine of incorporation, which gradually applied the Bill of Rights to the states.

The doctrine of substantive due process, popular since the turn of the century in restricting states' rights to regulate economic activity, was also used to apply certain aspects of the Bill of Rights to the states under the subsidiary doctrine of fundamental rights -- rights so engrained in the essence of America that they could not be denied by the states without simultaneously denying the right of due process guaranteed by the Fourteenth Amendment. Beyond these fundamental rights, the states were free to ignore the provisions of the first eight Amendments.

When accused murderer Palko was convicted of second-degree murder by a Connecticut jury which had reduced the charge from capital murder, the prosecution elected to appeal the case, a move permitted by that state's laws. In the second trial, Palko was convicted of the higher crime, and sentenced to death. He appealed the conviction on the claim that he had been subjected to double jeopardy, a violation of his Fifth Amendment rights. In addition, he charged that the second, stiffer sentence violated his Fourteenth Amendment right to due process.

Relying on dissents in the earlier cases of Twining v. New Jersey (1908) and Hurtado v. California (1884), Palko claimed that the Fourteenth automatically incorporated the Bill of Rights requirements and made them applicable to the states, thus giving him Fifth Amendment protection in his murder case.

The Supreme Court was not yet ready for this logic, and rejected Palko's appeal. In writing for the majority, Justice Benjamin Cardozo accepted that there was a trend towards applying additional aspects of the Bill of Rights to the states, but rejected the notion that the Fourteenth Amendment automatically incorporated any portion the Bill. The Due Process clause required the states to recognize only those rights which were so fundamental as to represent "the very essence of a scheme of ordered liberty." The Court had previously found guarantees such as free speech, assembly and religion to be among such fundamental rights.

Justice Cardozo further found that the Fifth Amendment guarantee against double jeopardy was not such a fundamental right, and should not prevent a state, under its laws, from appealing what it felt to be a faulty trial decision.

In another case decided in 1937, West Coast Hotel v. Parrish, the Court rejected the previously unrestrained use of substantive due process against state actions, and was therefore faced with finding a more carefully defined alternative to protect citizens' rights. Palko's timely reliance on the Due Process clause to protect fundamental rights may have been a key to the eventual solution, the very doctrine that Justice Cardozo had rejected, incorporation.

In the 1947 case of Adamson v. California, which reiterated the findings of Palko, Justice Hugo Black's dissent made the clear case for full and complete incorporation. Though the Court never accepted such a sweeping mandate, it nonetheless was pushed forward by the basic concept of incorporation and, in 1969, overturned Palko in Benton v. Maryland, ruling that the Due Process clause does, in fact, incorporate the double jeopardy restriction of the Fifth Amendment.