The U.S. Supreme Court case John Sullivan v. Louisiana in 1992 revolved around the issue of whether a constitutionally deficient reasonable-doubt instruction could be subjected to harmless-error analysis or not. The petitioner, John Sullivan, was convicted for murder based on jury instructions that were later deemed unconstitutional as they lowered the prosecution's burden of proof below what is required by the Due Process Clause. The Louisiana Supreme Court upheld his conviction stating that this error was harmless beyond a reasonable doubt since there was overwhelming evidence against him. However, when appealed to the U.S Supreme Court, it unanimously reversed this decision arguing that such an error can never be considered harmless because it vitiates all factual findings and thus deprives defendant’s right of trial by jury who would determine guilt beyond a reasonable doubt.

In the dissenting opinion for John Sullivan v. Louisiana, Justice Scalia argued that while the jury instruction given was indeed erroneous under Cage v. Louisiana, it did not necessarily render Sullivan's trial fundamentally unfair or unreliable in determining guilt or innocence. He contended that a harmless-error review should have been conducted to determine if the incorrect instruction had any actual impact on the verdict. Scalia believed this case presented an opportunity to clarify when constitutional errors could be deemed harmless and disagreed with automatically reversing convictions due to certain types of errors without considering their actual effect on outcomes.