To be sure, predicting how Supreme Court justices will vote based upon the questions asked during oral arguments is the legal equivalent of reading tea leaves. But after four full hours of Supreme judicial inquiry and carefully crafted responses in the constitutional challenges to the Bipartisan Campaign Reform Act of 2002, a.k.a. BCRA or McCain-Feingold, the overwhelming impression left on the informed Court watcher had to be that, once again, the single vote that mattered sat to the immediate left of Chief Justice William Rehnquist. And that vote, properly addressed, is Justice Sandra Day O’Connor.

Vigorous and pointed questioning at Monday’s special session seemed to expose a down-the-middle split amongst the other eight justices – assuming that the ever-silent Justice Clarence Thomas continues to adhere to his previously stated position, shared with Justice Antonin Scalia, that all "campaign finance laws are subject to strict scrutiny" and that "‘broad prophylactic caps on … giving in the political process … are unconstitutional’" under the First Amendment.

On the one side sits Chief Justice Rehnquist who, along with Justices Scalia, Anthony Kennedy, and the tacit Thomas, suggested, "I don’t think" the quarter century old landmark campaign finance decision in Buckley v. Valeo, 424 U.S. 1 (1976), "supports the proposition that Congress can willy nilly regulate any sort of contributions in connection with an election campaign."

Justice Scalia went even farther, asking Solicitor General Theodore Olson, who was defending the restrictions as the federal government’s lead attorney: "There are certain absolutes, aren’t there, even if problems subsist? There are just some things the government can’t do?" Then, quoting the First Amendment, Justice Scalia explained exactly what he meant. "[L]et’s start with the text. ‘Congress shall make no law … abridging the freedom of speech.’ … These laws abridge the freedom of speech in some sense. Now, on what basis do you think there is somehow a way around that text?" he questioned.

Chief Justice Rehnquist apparently agreed, acknowledging that, although he had approved of campaign finance limitations in the past, "it seemed to [him] since [those votes] that the whole purpose of the First Amendment is to allow people who perhaps don’t have much in the way of public opinion to try to change public opinion."

There was also the other camp of four justices, led by Justice Stephen Breyer, and including Justices John Paul Stevens, David Souter, and Ruth Bader Ginsburg, whose questions assumed that Congress could properly block private money from flowing to political candidates through constitutional "loopholes."

For instance, Justice Breyer got into the argument early by rationalizing the law in stating, "I gathered the statute was passed because, let’s call him Joe Wealthy, wants to write a check for $10 million to help his favorite candidate Smith get elected. And they figured out a way, who ‘they’ is is named in the lower court opinion, but we'll just say ‘they.’ They figured out a way despite the prior law to do it. It would pay for get out the vote, it would pay for voter registration, and it would pay for issue ads which didn’t say ‘Vote for Smith.’ What they said was Jones, his opponent, is a real rat, go tell him what you think of him, okay. I mean … that was the problem."

Justice Stevens agreed Congress should be able to act and questioned why the line between protected and unprotected political advocacy should be drawn at whether the words chosen expressly advocated the election or defeat of an identified candidate – the constitutional touchstone set forth in the Buckley case. "[W]hy should a speech urging [voters] expressly to elect a particular candidate to [be] President of the United States, why should that speech be entitled to less constitutional protection than a speech urging the ratification of the Panama Canal Treaty, for example?" he asked.

Justice Ginsburg had the same concern. "Do you recognize that express advocacy is the easiest thing in the world to avoid?" she asked noted First Amendment attorney Floyd Abrams, who was challenging the law. "You just say everything about how great your candidate is or how terrible the opponent is, except [you don’t say] ‘go to the polls and vote for X,’" she argued.

Which leaves Justice O’Connor, and what would be the decisive fifth vote.

Much has been made of the role Justice O’Connor plays on the High Court – that of the perennial swing vote. In fact, in recent terms, more than a few practitioners, commentators and Court watchers have joked, tellingly, that this is, in reality, the "O’Connor Court" – replacing the traditional identifying use of the sitting chief justice’s name with that of the justice whose vote is so valuable it virtually guarantees a Supreme win. But Justice O’Connor’s position at the center of the nine-member Court is more than just an affectation for being the Court’s decisive voice. Justice O’Connor’s jurisprudence has typically been carefully calculated, designed to pay due deference to precedent and to break new legal ground only when necessary.

Her trepidation and uneasiness with wholly rewriting campaign finance law was noticeable on Monday, even as other justices, such as her frequent voting partner Justice Kennedy, openly suggested that the constitutional distinctions set forth in Buckley and its progeny were "meaningless" and that the Court should "just junk it and begin anew."

Justice O’Connor wasn’t interested in beginning anew or even in the overarching principles of the First Amendment and federalism. Instead, Justice O’Connor was, once again, focused on the facts of the case and, from all appearances, whether she could reach a decision without making any new law at all.

In the unusually few questions that she asked, Justice O’Connor steered the arguing attorneys away from broad principles, instead focusing Solicitor General Olson on whether the evidence supported Congress’ reasons for BCRA’s political speech restrictions and then making sure Abrams was not taking the position that Congress was unable to regulate election-related advertising at all. In short, Justice O’Connor used Monday as yet another opportunity to take a page right out of her decision in Planned Parenthood of Southeastern Pennsylvania v. Casey, 505 U.S. 833 (1992), where she forcefully articulated her position of stare decisis, or following past decisions, absent extraordinary circumstances.

It may seem strange that a decade-old case that was fought over the continuing vitality of Roe v. Wade could play such a big role in the constitutionality of the McCain-Feingold campaign finance restrictions, but Justice O’Connor’s Casey opinion sets forth in clear terms the road map she follows in narrowly deciding controversial, and hotly disputed cases of constitutional importance – most recently in the affirmative action cases brought against the University of Michigan.

In the Casey case, Justice O’Connor explained that a landmark constitutional decision should only be overruled when its "central rule has been found unworkable; whe[n] the rule’s limitation on state power could be removed without serious inequity to those who have relied upon it or significant damage to the stability of the society governed by it; whe[n] the law’s growth in the intervening years has left [the decision’s] central rule a doctrinal anachronism discounted by society; and whe[n the decision’s] premises of fact have so far changed in the ensuing … decades as to render its central holding somehow irrelevant or unjustifiable in dealing with the issue it addressed."

None of these factors support overturning the landmark Buckley decision and its central First Amendment holding, and so, just maybe, Justice O’Connor will do what she does best and again vote to reaffirm yet another landmark constitutional rule – namely, Buckley’s central holding that, for a restriction on election-related speech to be constitutionally valid, "it must be construed to apply only to expenditures for communications that in express terms advocate the election or defeat of a clearly identified candidate for federal office." And if that’s how Justice O’Connor casts the fifth deciding vote, McCain-Feingold will fall, not by "beginning anew," but by relying on a case that’s been tried and true.