First, Chief Justice John Roberts is — or should be — concerned about the steadily-declining standing of the Court in the public’s mind, along with the growing perception that the justices decide according to partisan politics rather than according to legal principle. The 5-4 decision in Citizen’s United, for example, looked to all the world like a political rather than a legal outcome, with all five Republican appointees finding that restrictions on independent corporate expenditures violate the First Amendment, and all four Democratic appointees finding that such restrictions are reasonably necessary to avoid corruption or the appearance of corruption. Or consider the Court’s notorious decision in Bush v. Gore.

The Supreme Court can’t afford to lose public trust. It has no ability to impose its will on the other two branches of government: As Alexander Hamilton once noted, the Court has neither the purse (it can’t threaten to withhold funding from the other branches) or the sword (it can’t threaten police or military action). It has only the public’s trust in the Court’s own integrity and the logic of its decisions — both of which the public is now doubting, according to polls. As Chief Justice, Roberts has a particular responsibility to regain the public’s trust. Another 5-4 decision overturning a piece of legislation as important as Obamacare would further erode that trust.

It doesn’t matter that a significant portion of the public may not like Obamacare. The issue here is the role and institutional integrity of the Supreme Court, not the popularity of a particular piece of legislation. Indeed, what better way to show the Court’s impartiality than to affirm the constitutionality of legislation that may be unpopular but is within the authority of the other two branches to enact?