Justice Antonin Scalia holds himself out as the patron saint of originalism, the idea that judges should interpret the Constitution according to its original public meaning. To do otherwise, he adds, is to succumb to government by black-robed philosopher-kings who fill the empty vessel of a “living Constitution” with their own policy preferences.

Last week, however, in a case building on Scalia’s own landmark opinion in District of Columbia v. Heller — which found that the Second Amendment protects an individual right — when the justice was faced with a golden opportunity to advance originalism, he blinked. And in rejecting originalism, Scalia cited the un-originalist reason that following a different — and clearly incorrect — line of precedent was “easier.”

The case at issue, McDonald v. Chicago, involves a challenge to Chicago’s gun ban and seeks to extend the right to keep and bear arms to the states — as nearly all other provisions in the Bill of Rights have been extended.

The Court could take two possible routes, both under the Fourteenth Amendment, to apply, or “incorporate,” the Second Amendment right against the states: the Due Process Clause and the Privileges or Immunities Clause.

Scalia has long crusaded against the former, which encompasses the “substantive due process” doctrine. To Scalia, this doctrine — which has protected rights based on alleged constitutional “penumbras and emanations” — embodies the judicial activism that is the bane of his jurisprudence. Scalia has attacked substantive due process as an “atrocity,” an “oxymoron,” “babble,” and a “mere springboard for judicial lawmaking.”

Largely as a response to this sort of “judicial usurpation,” Scalia has advanced his theory of originalism. To interpret the Fourteenth Amendment, for example, a judge should look at how the amendment was understood at the time of its ratification in 1868.

McDonald presents originalist judges the perfect chance to restore the original meaning of a long-abused constitutional provision: In 1873, a Supreme Court unwilling to accept Reconstruction-era changes to our constitutional order — with the federal government empowered to check state oppression — eviscerated the Privileges or Immunities Clause. By reinvigorating that clause, the Court can scale back a warped Due Process Clause that has been misused in a clumsy attempt to protect individual rights.

Without the Privileges or Immunities Clause, however, the Court must continue extending the un-originalist version of substantive due process to protect the right to keep and bear arms. To give original meaning to the Second Amendment, it must ignore the original meaning of the Fourteenth Amendment!

Yet this is the line Scalia took last week: Instead of accepting the plain meaning of the Privileges or Immunities Clause — which uncontrovertibly protects the right to keep and bear arms — the justice chose a route that avoids disturbing a 140-year-old precedent rejected by legal scholars of all ideological stripes.

In 2008, Scalia wrote, “It is no easy task to wean the public, the professoriate, and (especially) the judiciary away from [living constitutionalism,] a seductive and judge-empowering philosophy.” But at the arguments in McDonald, he argued that while the Privileges or Immunities Clause “is the darling of the professoriate,” he would prefer to follow substantive due process, in which he has now “acquiesced,” “as much as [he] think[s it is] wrong.”

Given Scalia’s epic enmity for substantive due process, why would he now turn his back on decades of his own hard labors and suddenly endorse the controversial doctrine? In his own words, because it is “easier.”

Granted, Scalia has been far from a down-the-line originalist. On more than one occasion, where originalism does not achieve the result he wants, he ignores the history and stands by precedent. (Most recently, Scalia voted to uphold the federal power to trump state regulation of medicinal marijuana, even if the drug never crosses state lines.) To explain these variances, Scalia has called himself a “faint-hearted originalist” or an “originalist, but not a nut.”

But if the opinion Scalia joins in McDonald matches his signals at argument, the justice will no longer be able to call himself an originalist of any kind. He will have to turn in his O‑card and leave Clarence Thomas as the only originalist on the Court. (Not coincidentally, Thomas is the only justice on record as favoring a revival of the Privileges or Immunities Clause.)

The Court has nearly four months before it issues its McDonald opinion. We can only hope that the straying Saint Originalism returns to the catechism he has taught so well.