In his White House memoir, “Courage and Consequence,” Karl Rove recalls being the lone non-lawyer among the group of George W. Bush aides who initially interviewed John Roberts for the Supreme Court in 2005. Rove asked Roberts to go back in history to name the justice whom he most revered. Roberts’ answer, Robert Jackson, intrigued and reassured Rove. When appointed in 1941, Jackson was serving as Franklin Roosevelt’s attorney general and had been expected to be a pro-New Deal rubber-stamp on the court. But, as Rove put it, Jackson “instead demonstrated a fidelity to the Constitution that Roberts admired.”

Thursday, in a jaw-dropping turnabout worthy of Justice Jackson, Roberts provided the swing vote in a 5-to-4 decision that upheld the constitutionality of almost all of Obamacare, the president’s signature legislative achievement. While an army of armchair court watchers expected Justice Anthony Kennedy to determine the fate of the Affordable Care Act (a recent Time cover called him “The Decider”), it was Roberts who took his fidelity to the Constitution in an ideologically surprising direction. Kennedy voted with three other conservative justices to overturn the health insurance mandate at the heart of the law.

Constitutional law seminars and unlicensed political psychologists will spend years speculating about Roberts’ motivations in joining the liberal bloc in probably the most important Supreme Court decision since Bush v. Gore in 2000. While we may wait decades to know for certain, it does seem plausible that Roberts may have been partly triggered by a desire to prevent the court from being seen as overtly political. Polls showing public respect for the Supreme Court at a quarter-century low reflect the growing view that the justices pursue partisan agendas.

One of the most important passages in Roberts’ majority decision was the chief justice’s assertion: “We do not consider whether the act embodied sound policies. That judgment is entrusted to the Nation’s elected leaders. We ask only whether Congress has the power under the Constitution to enact the challenge provisions.”

In short, if you want a national referendum on the health-care law, then the proper arena is the 2012 campaign—and not the inner sanctums of the Supreme Court.

The majority opinion in the health care case points up the inadequacy of the political clichés used in the heat of an election year to describe the Supreme Court. Phrases like “strict constructionist” and “not making law from the bench” do not clarify complex Supreme Court opinions like Thursday’s ruling. Romney’s campaign website declares, “As president, Mitt will nominate judges in the mold of Chief Justice Roberts and Justices Scalia, Thomas and Alito.” There’s only one problem with this formulation: Roberts went in one direction and Scalia, Thomas and Alito went in the opposite on the constitutionality of the health care bill.