Jill Elaine Hasday is Distinguished McKnight University Professor and Centennial Professor of Law at the University of Minnesota Law School. She is the author of "Family Law Reimagined."

Republican presidential candidate Donald Trump gestures at a news conference near the U.S.- Mexico border outside of Laredo, Texas. (Rick Wilking/Reuters)

This week, Donald Trump’s lawyer Michael Cohen reportedly said: “You cannot rape your spouse. And there’s very clear case law.” The comment ricocheted around the Internet and was denounced by scores of critics, who accused Cohen of misstating the law. He’s since apologized.

Unfortunately, Cohen’s broad declaration was less wrong than we’d like to think. All states prosecute some forms of marital rape in theory. But in reality, statutes criminalizing marital rape are often inadequate. They also remain dramatically and disproportionately under-enforced.

This injustice has deep historical roots. For centuries, husbands were absolutely exempt from criminal prosecution for raping their wives. In the eyes of the law, marital rape was a legal impossibility.

That is no longer true. Starting in the 1970s and 1980s, every state eliminated husbands’ absolute immunity from prosecution. Most states accomplished this reform through legislation. A few achieved it through judicial opinions.

In 1984, the New York Court of Appeals held that Mario Liberta could be prosecuted for raping his wife (which he had done in the presence of their two-and-a-half-year-old son). The court concluded that the state’s marital rape exemption violated equal protection requirements because there was no rational reason to distinguish between marital and non-marital rape.

[The ancient, sexist roots of what Donald Trump’s adviser said about rape]

Yet modified forms of the marital rape exemption survive in at least 23 states. Legislatures in these states continue to treat rape in marriage more leniently than rape outside of it. Some  criminalize a narrower range of conduct if committed within marriage, others impose less serious penalties on the marital rape they do recognize or create special procedural obstacles to marital rape prosecutions.

For example, in South Carolina a married person living with his spouse cannot be convicted of criminal sexual conduct even if he or she “uses force or coercion to accomplish the sexual battery” of the spouse, so long as there are no other aggravating circumstances.  In Virginia, the law includes special provisions making probation, rather than prison, an option for convicted marital rapists.

Marital rape exemptions persist for at least two reasons. First, legislatures remain committed to these exemptions, despite more than a century of reform efforts from women’s rights activists. Second, the Supreme Court’s constitutional jurisprudence on sex discrimination generally limits itself to scrutinizing laws that draw explicit distinctions between women and men. Once states in the late 20th century rewrote their marital rape laws to focus on “spouses” rather than husbands and wives, most lower courts concluded that laws treating marital rape more leniently posed no constitutional problem.

All the available evidence indicates that the victims of marital rape are almost exclusively female. The Supreme Court’s interpretation of the Constitution places great weight on the formal distinction between sex-neutral and sex-specific language. But as a practical matter, both kinds of marital rape exemption have almost the same effect. Today, as in the nineteenth century, married women do not enjoy the criminal law’s full protection from rape.

Rather than criticizing Cohen for missing the nuances of marital rape exemptions, we should focus on changing the law. On the question of marital rape, family law’s historical roots in inequality remain persistently visible.