In the 1970 case Younger v. Harris, the U.S. Supreme Court ruled that federal courts should abstain from interfering in ongoing state criminal prosecutions unless there is proven bad faith or harassment by state officials, or a statute being challenged is "flagrantly and patently violative of express constitutional prohibitions." The case arose when John Harris Jr., who was charged under California's Criminal Syndicalism Act for making speeches supporting violence as a means of achieving political change, sought to restrain District Attorney Evelle J. Younger from prosecuting him on grounds that the act violated his First Amendment rights. However, since he had not yet been tried nor convicted under this law at the time he filed suit in federal court seeking an injunction against its enforcement, it was determined that his challenge was premature and thus inappropriate for federal intervention.

In the dissenting opinion for Younger v. Harris, Justice William O. Douglas argued that federal courts should have the power to intervene in state prosecutions when constitutional rights are at stake. He disagreed with the majority's reliance on principles of equity and comity, asserting instead that these doctrines should not be used as barriers to prevent individuals from seeking federal relief against potentially unconstitutional state actions. Douglas contended that it was inappropriate for a defendant to have to risk conviction before being able to challenge a statute’s constitutionality; he believed this could deter people from exercising their First Amendment rights due to fear of prosecution under an overbroad law. Furthermore, he criticized the majority's decision as undermining previous Supreme Court rulings which allowed intervention by federal courts in certain circumstances involving ongoing state proceedings.