Chief Justice Roberts' opinion was clearly motivated at least in part by a desire to protect the Court from partisan attacks and the concomitant erosion of the respect it enjoys, which is key to its power and influence. (Charles Krauthammer). But Roberts' concern in this regard was clearly exaggerated and out of proportion to the real risk (John Yoo), and it was definitely heightened by Obama's recent political attacks on the Court.
Roberts' decision is yet another example of the attacks of weakness observable among Washington conservatives (including some on the Supreme Court), which is to be contrasted with the dependable boldness of Leftists, who maximally utilize every branch of the federal government, public opinion be damned, to advance their agenda: e.g., the Court (Roe, Lawrence), the Congress (Obamacare) and the Presidency (Obama's lawless deportation order).
I'm stuck somewhere between belief and hope, that Roberts' decision is indicative of a misplaced concern for the Court's public image, and a desire to undermine the Left's scurrilous slander that the Court majority has become an arm of the Republican Party, and, more importantly, a desire to give himself room on future decisions.
I do not think (and hope I'm right) that the decision is indicative of a more systemic wobbliness by Roberts, a la Powell or even Kennedy.
I am between belief and hope.