Well, several things. Blackmun was perhaps the most prominent in a line of ideological apostates (i.e., Republican appointees who took a left turn) that stretched from him to John Paul Stevens to David Souter and includes (in much lesser measure) Sandra Day O’Connor and Anthony Kennedy. Though a Nixon appointee, he went on to write Roe v. Wade, and over time staked out positions that resonated with liberal policy views on issues like affirmative action and the death penalty. But it wasn’t just what Blackmun said; it was the way he said it. Perhaps things will look different decades from now, but to contemporary eyes, it seems that today’s left-of-center Supreme Court justices crank out their opinions in prose that is narrow, technocratic, and mostly forgettable. (Who but the most committed constitutional law geek would recognize a single line from any of Stephen Breyer’s opinions?) By contrast, Blackmun knew how to speak a different language–one that was deeply moral, forceful, and humane. Sometimes he could be highly personal. When, after decades of deliberation, he decided in 1994 to renounce capital punishment he proclaimed: “I no longer shall tinker with the machinery of death.” And when summing up the case of a sad little boy abused by his father into profound retardation while local authorities dithered, Blackmun went right to the heart of the matter. “Poor Joshua!” he famously wrote.

But for all his attractive qualities, Blackmun’s jurisprudence has left a mixed legacy for liberals. The legal solidity of Roe has been questioned by both the right and the left, and political shocks created by the opinion have not been an unalloyed blessing to the Democratic Party. Even fans of the policies that undergird much of Blackmun’s jurisprudence may be forgiven for asking: Did he strike the right balance between head and heart? Or, upon solemn reflection, might even liberals conclude that Blackmun reached too far with Roe, that his opinions could be too personal and impassioned, and that the left is possibly better off with the dryly competent–if not especially inspired–style of today’s liberal justices? Disappointingly, Linda Greenhouse’s new biography, Becoming Justice Blackmun, fails to wrestle with these questions, but her well-paced and accessible treatment of Blackmun’s life is a useful place to begin the inquiry.

So, who was Harry Blackmun? As Greenhouse describes, he was an up-by-the-bootstraps son of a struggling Twin Cities merchant, who found his way, through grit and merit, to Harvard Law School. (Point of grade inflation trivia: Blackmun graduated near the top quarter of his law school class with three Ds and eight Cs on his transcript.) He was also a medicine buff and worked a professionally very satisfying mid-life stint as counsel to the Mayo Clinic.

But perhaps the single most striking feature of Blackmun’s biography is that, for most of his life, he was great friends with Warren Burger. The Blackmun-Burger friendship began in elementary school (the boys lived just six blocks from each other in St. Paul’s Dayton’s Bluff neighborhood) and strengthened as the two men reached maturity, consistently coaching and encouraging each other to ever higher levels of achievement. For most of their careers, Blackmun and Burger were both personally and ideologically compatible; as federal appellate judges, both were wary about liberal trends in the law and exhibited a penchant for deference to the legislative branches. Indeed, they seemed so similar that when Nixon appointed them to the Supreme Court in rapid succession, the press dubbed them the “Minnesota Twins.” But that all started to change with Roe v. Wade.

The irony, as Greenhouse suggests, is that the relatively conservative Chief Justice Burger personally selected his friend Blackmun to write the Roe opinion–probably at least in part because (personally respecting Blackmun’s medical acumen) the Chief thought he could count on Blackmun’s sense of judicial modesty to keep the opinion narrow.

The central question in Roe concerned the constitutionality of a Texas statute that made abortion a crime except when it was necessary for “the purpose of saving the life of the mother.” It was clear that a majority of the Court (including Burger and a third Nixon appointee, Lewis Powell) thought that the statute was impermissibly vague in the guidance it gave doctors about how to treat their pregnant patients. A simple opinion overturning the Texas law for vagueness was likely what Burger had in mind. But if the opinion didn’t come out that way, it wasn’t wholly Blackmun’s doing. In fact, Blackmun’s first draft was quite narrow and said nothing about whether women have a constitutionally protected right to obtain abortions.

The more liberal wing of the Court was not satisfied, however, so Blackmun went back to the drawing board, and months later (after, among other things, a research trip to Mayo), he developed an opinion which found that abortion procedures were covered by the constitutionally protected right of privacy. And even then there had to be adjustments. Blackmun at first suggested that the constitutional protection should extend with certainty only until the end of the first trimester, but he was rather easily persuaded by Justice Powell to move the mark to two trimesters. When it was finally issued in January 1973, the 7-2 Roe opinion had many of the qualities of a work drafted by committee.

But even if Roe was the product of many hands, Blackmun claimed it as his own and worked staunchly to defend it–and, in doing so, his old habits of judicial modesty began to slip away. When cases came along that probed the implications of Roe–questioning, for example, whether states could withhold public funding for abortions, regulate the advertising of abortion services, or restrict abortions for minors–Blackmun almost invariably voted for the result that would expand access to abortions. Moreover, Greenhouse contends that it was these post-Roe battles (which Blackmun often lost) that transformed his jurisprudence on everything from poverty–an issue he was forced to confront in the state funding cases–to women’s rights. His jurisprudence on matters like affirmative action and the death penalty changed, too.

As a measure of Blackmun’s ideological drift, Greenhouse notes that in their first five terms on the Court, Blackmun voted with Burger on 87 percent of close cases; during their last five years together, the figure was down to 32 percent. But while Blackmun’s ideological evolution is striking, Greenhouse’s explanation for it is somewhat lacking in ambition, and amounts to little more than a handful of statements like the following: “Warren Burger could never have suspected that in turning to his reliable friend for [the Roe opinion], he was launching Blackmun on a journey that would open him to new ideas and take him far from their common shore of shared assumptions.”

As analysis goes, this is hardly satisfying. For one thing, Greenhouse asks the reader to take at face value the suggestion that Blackmun’s conversion was simply a matter of encountering liberal ideas and deciding–mirabile dictu–that they were right. Maybe that was part of it, but when a person changes his entire judicial philosophy to the extent Blackmun apparently did on the Court, isn’t there likely to have been something more at play? One can imagine, for example, that there might have been a liberal feedback effect at work–in that Blackmun wrote an iconic liberal opinion (Roe), received the adoring attentions of liberals, no doubt attracted increasingly liberal clerks, and probably found himself in a reinforcing leftward spiral. Or perhaps there was something about being on the Supreme Court that conferred on Blackmun a sense of urgency–a sense that the policy issues being decided were just too important for him to defer to principles of judicial modesty. Or perhaps it was something else. Whatever the case, a book like this should be looking harder for the answer.

Part of the problem here is that Greenhouse has relied almost exclusively on Blackmun’s own papers in writing Becoming Justice Blackmun–a choice that dramatically constrains her ability to bring critical perspective to the book. It’s a real shortcoming. For readers who are already taken by Blackmun’s jurisprudence, and do not wish to have their views unsettled, Becoming Justice Blackmun will be a fun and comfortable read. For the rest, there is some interesting information, but precious little insight that will change attitudes or help liberals evaluate what they should be looking for in their judges. Right now, figuring out whether they would prefer more Blackmun-style justices or Breyer-style justices on the Supreme Court is not exactly the biggest issue facing the Democrats. But someday that kind of question will be relevant again. By then, perhaps a clearer picture of Blackmun’s legacy will have emerged.