As Bill Clinton’s case goes to the Senate, the details of those long-ago days are relevant again. For people trying to sort through what happened back then–and what may unfold in the coming season–there is no better guide than a hitherto-obscure 1992 book called ““Grand Inquests: The Historic Impeachments of Justice Samuel Chase and President Andrew Johnson.’’ Its author? William H. Rehnquist, the chief justice of the United States, who will preside over the Senate proceedings. (A paperback reissue is in the works.) There are obvious differences between that time and this: Clinton is popular, some senators–even Republicans–are desperate to avoid a trial and there is no single great divisive national issue. Still, the book casts light on the enduring partisan impulse in American politics–and on how Rehnquist may view a trial.

Johnson, a Southern Democrat who became president in 1865 after Lincoln’s assassination, incurred the rancor of Republicans because of his opposition to harsh post-Civil War Reconstruction. Looking for any pretext to get rid of the new president, the Radical Republicans–who considered Johnson, a Tennessean, too soft on the defeated Confederates–impeached him after he fired War Secretary Edwin M. Stanton in February 1868. Their grounds? That Johnson had violated the Tenure of Office Act, a constitutionally questionable law that said a president could not dismiss members of the cabinet without Senate approval.

During the trial the quick-tempered Johnson tried going about the business of running the government, labeling his accusers scoundrels in the treasonous tradition of Benedict Arnold. But for all practical purposes the trial brought Washington to a halt. The president was convinced the Radical Republicans were waging a coup d’etat: ““Damn them!’’ he exploded. Johnson’s predicament was so grim that on the closing day of the trial the New York Tribune saw fit to run the headline CONVICTION ALMOST A CERTAINTY. Though Johnson escaped conviction by a single vote on each of the two counts, Radical Republicans had achieved their political goal: they humiliated Johnson and derailed his pro-Southern policies.

The good news for Clinton is that Rehnquist considers the Senate’s failure to convict Johnson a constitutional watershed that did much to strengthen the independence of the presidency and the judiciary. As Rehnquist concludes, the constitutional significance of Johnson’s acquittal ““can hardly be overstated,’’ for it saved ““the American system of government’’ from the sort of congressional supremacy that was feared by the Founding Fathers. ““Grand Inquests’’ illuminates Rehnquist’s firm belief that partisan differences alone are insufficient predicates for removing a high official from office. True, the central issue in Clinton’s case is perjury, but one White House defense may be that the questions about Monica Lewinsky in the Paula Jones case were essentially politically motivated. And readers of ““Grand Inquests’’ will quickly conclude that the chief justice does not take kindly to partisan legislators who want to inflict damage on the presidency for political reasons. Rehnquist may be a Nixon-Reagan court appointee, but his loyalty is to what he deems the constitutional framers’ ““original contributions’’ to the ““art of government’’–a robust presidency and a neutral judiciary.

But Clinton should not get cocky. Rehnquist’s disdain for drawn-out cases and pettifoggery by lawyers is legendary. So while he’ll run a brisk, bland show that won’t unduly embarrass the president, he dislikes sophistry and hairsplitting–two things that the president’s team may fall back on. Such a maneuver will be risky, for the chief justice’s historical writings and his judicial reputation make one thing clear: he not only doesn’t suffer fools lightly, he refuses to suffer them at all. That no-nonsense rigor might have sped up Johnson’s trial–and will almost surely be a hallmark of Clinton’s.