The Supreme Court, as expected, announced Monday that it will review the constitutionality of President Obama’s health-care-reform law. A decision is likely by next June. In the intervening months, we will be informed many times that the issue in the case is whether the requirement that individuals buy health insurance from private companies violates the Commerce Clause of Article I.

Don’t believe it—at least not completely. In a case of this magnitude, a technical reading of the Constitution and laws is only one factor that goes into the Justices’ determination. More fundamentally, this case, like any big case, will be about power.

Two new books offer a timely reminder of how the interaction between the President and the Supreme Court work in the real world. Jeff Shesol’s “Supreme Power,” which was published last year, and James F. Simon’s “FDR and Chief Justice Hughes,” which will be released next February, both tell the story of the epic clash between Franklin Roosevelt and the Court over the New Deal. The books differ; Shesol is more sympathetic to F.D.R., while Simon takes Hughes’s side. But both books recognize the central role of Justice Owen Roberts, who was the swing vote of his day.

To review: In 1935 and 1936, a conservative majority on the Supreme Court, including Roberts, struck down a series of important New Deal initiatives, including the National Recovery Act and the Agricultural Adjustment Act. In response, following his landslide reëlection in 1936, Roosevelt proposed his court-packing plan, which would have expanded the number of Justices and thus given his appointees a clear majority on the Court. Around the time the plan was pending, Roberts started voting to uphold F.D.R.’s bills, and the court-packing plan died an unmourned death. It was, as the legend has it, “the switch in time that saved the nine.”

Shesol and Simon embroider the legend with fact. It’s clear, for example, that Roberts actually first voted with Roosevelt before the court-packing plan came to light. Still, the larger point remains true. Roberts saw how the country was changing—he saw that the New Deal had become a political and economic fact of life—and he decided to stay out of the way of history.

That’s a lesson for today. The current swing vote, of course, is Anthony Kennedy, and it is difficult to imagine health care being upheld without his support. Kennedy is an ethical and honorable man, but there’s no doubt that he, too, follows the news. All the Justices do. The case will be argued next February or March, when all of us will have a better idea of whether President Obama will be reëlected. If Obama looks like a lame duck at that point, it will be a lot easier for the Justices to dismantle his signal achievement; if Obama looks like a winner, some on the Court may think twice about picking this particular fight with him.

To a great extent, that’s what happened with George W. Bush in the Supreme Court, especially when it came to the central events of his Presidency, the war on terror and the Iraq war. The Court did make a series of measured rulings against Bush on the issue of the detainees at Guantánamo when he was facing reëlection in 2004, but the Justices, especially Kennedy, really turned on him when the war went south. The Hamdan v. Rumsfeld (2007) and Boumediene (2008) cases clearly owe something of their contemptuous tone to the failed nature of the Bush Presidency. Like voters, the Justices smell weakness, and respect strength. No one likes a loser.

Recent auguries have looked promising for the fate of health care in the Supreme Court. As challenges to the law have worked their way through the lower courts, political form has mostly held; judges appointed by Democratic Presidents have tended to uphold the law, and judges named by Republicans have voted it down. But two recent exceptions to that rule have certainly drawn the attention of the Justices. Jeffrey Sutton, a former law clerk to Antonin Scalia, wrote the opinion upholding the law in the Sixth Circuit, and Laurence Silbermann, a widely respected conservative, wrote a powerful endorsement of its constitutionality in the D.C. Circuit.

It all goes to show that sometimes (often) you don’t need a law degree to know how the Supreme Court is going to vote—just know which way the wind is blowing.

Photograph by Mark F. Sypher/Roll Call/Getty Images.