Courage, Orin ! Your question was a good one and Jack did not answer it. He draws an artificial distinction between questions of constitutional legitimacy ("Rather, living constitutionalism is primarily a theory about the legitimacy of the constitutional system taken as a whole: how and why constitutional doctrine changes in a way that preserves its legitimacy over time.") and questions about how justices should decide cases. He insists the questions are separate, but they are not--at least, not if the justices care about the legitimacy of the constitutional system, as they most certainly do. Here's Justice O'Connor ( Planned Parenthood v. Casey ), who even uses the word "legitimacy" over and over again.
The root of American governmental power is revealed most clearly in the instance of the power conferred by the Constitution upon the Judiciary of the United States, and specifically upon this Court. As Americans of each succeeding generation are rightly told, the Court cannot buy support for its decisions by spending money, and, except to a minor degree, it cannot independently coerce obedience to its decrees. The Court's power lies, rather, in its legitimacy, a product of substance and perception that shows itself in the people's acceptance of the Judiciary as fit to determine what the Nation's law means, and to declare what it demands.
The underlying substance of this legitimacy is of course the warrant for the Court's decisions in the Constitution and the lesser sources of legal principle on which the Court draws. That substance is expressed in the Court's opinions, and our contemporary understanding is such that a decision without principled justification would be no judicial act at all. But even when justification is furnished by apposite legal principle, something more is required. Because not every conscientious claim of principled justification will be accepted as such, the justification claimed must be beyond dispute. The Court must take care to speak and act in ways that allow people to accept its decisions on the terms the Court claims for them, as grounded truly in principle, not as compromises with social and political pressures having, as such, no bearing on the principled choices that the Court is [505 U.S. 833, 866] obliged to make. Thus, the Court's legitimacy depends on making legally principled decisions under circumstances in which their principled character is sufficiently plausible to be accepted by the Nation.
... However upsetting it may be to those most directly affected when one judicially derived rule replaces another, the country can accept some correction of error without necessarily questioning the legitimacy of the Court.
... That first circumstance can be described as hypothetical; the second is to the point here and now. Where, in the performance of its judicial duties, the Court decides a case in such a way as to resolve the sort of intensely divisive controversy reflected in Roe and those rare, comparable cases, its [505 U.S. 833, 867] decision has a dimension that the resolution of the normal case does not carry. It is the dimension present whenever the Court's interpretation of the Constitution calls the contending sides of a national controversy to end their national division by accepting a common mandate rooted in the Constitution.
... So to overrule under fire in the absence of the most compelling reason to reexamine a watershed decision would subvert the Court's legitimacy beyond any serious question. ...
... It is true that diminished legitimacy may be restored, but only slowly. Unlike the political branches, a Court thus weakened could not seek to regain its position with a new mandate from the voters, and even if the Court could somehow go to the polls, the loss of its principled character could not be retrieved by the casting of so many votes. Like the character of an individual, the legitimacy of the Court must be earned over time. So, indeed, must be the character of a Nation of people who aspire to live according to the rule of law. Their belief in themselves as such a people is not readily separable from their understanding of the Court invested with the authority to decide their constitutional cases and speak before all others for their constitutional ideals. If the Court's legitimacy should be undermined, then, so would the country be in its very ability to see itself through its constitutional ideals. The Court's concern with legitimacy is not for the sake of the Court, but for the sake of the Nation to which it is responsible.
Jack himself has subterranean doubts about this distinction, which keep bubbling to the surface. "Giving advice to judges is not really the goal of the theory." "It is probably best not understood as a theory advising judges...." "It may not be advice directed to individual judges, or, if it is, it must be far more than that." It might not be intended as advice, but Jack's theory certainly has implications for judicial decisionmaking--not necessarily that justices should do the politics of the president that appoints them, but that they should do whatever is necessary to maintain the legitimacy of the system. Why he denies, or may deny this, I don't understand, either. And if the implications are odd or don't seem right, that will cast doubt on the theory, even though the theory itself is intended to answer an entirely different question, and even if Jack himself is not interested in the judicial advice question.