At the argument in the Mississippi case, concerning a state law that bans most abortions after 15 weeks, the chief justice refined that factor in an apparent attempt to dampen the jolt to the system.

He suggested that the fetal-viability line established in Roe was not a crucial part of the decision’s reasoning. “Was viability an issue in the case?” he asked. “I know it wasn’t briefed or argued.”

In shifting the focus from what the court had done to what the parties in the case had asked it to do, the chief justice was trying to justify upholding a 15-week line while stopping short of overruling Roe entirely, which would allow states to make all abortions illegal.

Whatever his goal, though, shifting the analysis from the words of the opinion to the advocacy that gave rise to it is a recent development and yet another way to undermine precedents.