John Roberts saves Obamacare: How does George W. Bush feel right now?

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.

Obama’s own ability at prophecy is limited, as well. In 2005, the former constitutional law professor declared in a Senate address that he was opposing Roberts’ nomination to the Supreme Court because “I ultimately have to give more weight to his deeds and overarching political philosophy … than to the assuring words he provided me in our meeting.”

While Obama has sharply disagreed with major decisions of the Roberts Court (particularly the anything-goes Citizen United ruling on campaign finance), it is tempting to wonder if the president now feels that he misjudged the man who saved his legislative legacy.

It is almost part of the job description of a president that he will make, at least, one blunder when picking Supreme Court justices. Harry Truman called one of his nominees, Tom Clark, a “damn fool from Texas.” When George H.W. Bush tapped New Hampshire jurist David Souter in 1990, the president never expected that he would be reinforcing the court’s liberal wing. Now it is Roberts who has refused to stay in his pre-determined ideological cubbyhole.

With four current justices over the age of 70, it is likely that whoever is elected president this November will get an opportunity to put his stamp on the Supreme Court. But the potential for Lucy-and-the-football surprises endures. About the only ways a president can achieve some measure of certainty about the court are either to nominate fire-breathing ideologues like Antonin Scalia or political cronies like Abe Fortas, who kept open a back channel to Lyndon Johnson during his brief tenure as a justice. But even the Scalia precedent no longer works, because anyone with a sharply articulated judicial philosophy probably could not make it through today’s hyper-partisan Senate.

As for the health care law, its major provisions remain on schedule to take effect in 2014. Even a President Romney may find it difficult to reverse history, as he would have to face down a filibuster threat by Senate Democrats to get a repeal bill through Congress. (There are, however, administrative gambits that Romney could use to eviscerate Obamacare if Congress proves balky.) That’s why the Supreme Court seemed like such a beguiling short cut for conservatives who loathe Obamacare.

It’s also why back in 2005 Karl Rove may have badly misinterpreted John Roberts’ stated intention to be an independent jurist like Robert Jackson.