Although many opponents of abortion would like to have no exceptions, even for the life of the mother, many others who oppose abortions generally insist that there be some exceptions. This latter group has a major problem, which is only beginning to surface: how to write an abortion ban that does not run afoul of the Supreme Court’s very strong rejection of criminal laws that are so vague that those subject to them cannot determine whether they have crossed the line from lawful to criminal.

The Supreme Court has made it clear, time and again, that the Due Process Clause precludes the government from enforcing vague criminal laws. As Justice Antonin Scalia ruled in 2015 in Johnson v. United States: “Our cases establish that the Government violates this guarantee by taking away someone’s life, liberty, or property under a criminal law so vague that it fails to give ordinary people fair notice of the conduct it punishes, or so standardless that it invites arbitrary enforcement.” The “void for vagueness” doctrine applies not only to the question of whether the accused has committed a crime, but also to whether a sentence enhancement applies, in that case because of the real uncertainty as to whether the defendant’s prior felony conviction “involves conduct that presents a serious potential risk of physical injury to another.”