History offers a lesson: There is a momentum to Supreme Court decisions, and efforts to cabin the logical progression of legal doctrine will fail if the political and cultural forces that led to the doctrine in the first place remain in play. It’s Newton’s law of motion in the legal context: A doctrine in motion will stay in motion unless met by an outside force — a backlash or a change of cast. The steps can be small, but they can add up to giant steps.

A recent example: the court’s endorsement of a doctrine known as the “ministerial exception,” which immunizes churches against lawsuits by clergy alleging job discrimination. The doctrine had been developed in the lower courts, and the Supreme Court considered it for the first time in 2012 with a unanimous opinion by Chief Justice Roberts. The question in Hosanna-Tabor Evangelical Lutheran Church v. Equal Employment Opportunity Commission was whether the exception applies to employees who are not ordained ministers and, if so, to whom. How far from the pulpit should the exception extend?

The court held that the exception applied to a parochial school teacher who claimed that her dismissal was the result of discrimination on the basis of disability. Although not an ordained minister, the teacher had special training and held the job title of “minister of religion, commissioned.” Church doctrine considered her to be a “called” teacher, as distinct from an ordinary “lay” teacher. She taught religion classes and led students in prayer. The court held that under the ministerial exception, her discrimination suit, whatever its merits, had to be dismissed. “There will be time enough to address the applicability of the exception to other circumstances if and when they arise,” Chief Justice Roberts wrote at the end of his opinion.

Inevitably, other circumstances did arise. Last week, the federal appeals court in New York applied the ministerial exception to the principal of a Catholic school in Rockland County, N.Y., dismissing the lawsuit she had filed alleging sex discrimination in the school’s refusal to renew her contract. Her job title was “lay principal,” and she had no formal training in religion or theology. Nonetheless, the appeals court concluded that her role in the school was that of a religious leader and that the ministerial exception therefore fit.

Writing for the three-judge panel, Judge Robert D. Sack acknowledged that the Supreme Court’s 2012 decision “is not without its Delphic qualities” and that the question was a hard one. The case “lies at the center of the tension between an employer’s right to freedom of religion and an employee’s right not to be unlawfully discriminated against,” he observed. The plaintiff’s lawyer said he would appeal to the full appeals court. If this case, Fratello v. Archdiocese of New York, doesn’t reach the Supreme Court, another one surely will as the boundaries of the ministerial exception are pressed ever outward.

Of course, not every decision gains momentum. The court’s 2008 decision interpreting the Second Amendment to protect the right to keep a handgun at home for self-defense is a case in point. The lower courts have refused many opportunities to extend the decision, District of Columbia v. Heller, beyond the original context. Maybe that’s because the 5-to-4 decision, overturning decades of implicit Supreme Court precedent, was such a shock to the system. Or maybe it’s because of the limits Justice Antonin Scalia set on his majority opinion. He made clear — probably in order to keep Justice Kennedy’s necessary vote — that the decision authorized handguns in the home and went no further:

Although we do not undertake an exhaustive historical analysis today of the full scope of the Second Amendment, nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms.

Last month, the court’s refusal to take up a case from California on whether the Second Amendment grants the right to carry firearms outside the home infuriated Justice Thomas, who accused his colleagues, with the exception of Justice Gorsuch, who joined him in dissent, of treating the Second Amendment as a “disfavored right.”

Someone could write a book about the Supreme Court’s failed footnotes, those that seemed to promise a limit on a decision’s holding that proves unable to withstand the momentum unleashed by the decision itself. One famous example is a footnote in Virginia Pharmacy Board v. Virginia Consumer Council, the 1976 decision that created the modern doctrine of commercial speech by granting pharmacists the First Amendment right to advertise drug prices. The logical question was whether the doctrine would apply to advertising by other professionals, including — horrors — lawyers. Justice Harry A. Blackmun added a footnote to his majority opinion that offered a kind of noncommittal reassurance:

We stress that we have considered in this case the regulation of commercial advertising by pharmacists. Although we express no opinion as to other professions, the distinctions, historical and functional, between professions, may require consideration of quite different factors. Physicians and lawyers, for example, do not dispense standardized products; they render professional services of almost infinite variety and nature, with the consequent enhanced possibility for confusion and deception if they were to undertake certain kinds of advertising.

Clear enough? A year later, in Bates v. State Bar of Arizona, another majority opinion by Justice Blackmun declared that lawyers have a First Amendment right to advertise.