Conservatives have had little to celebrate when the Supreme Court of the United States has handed down its most important decisions over the last four terms. 

As Georgetown Law Professor David Cole explains in a forthcoming law review article: "The Court upheld affirmative action in university admissions, ... reined in the 'federalism' revolution, frustrated the property rights movement, expanded criminal defendants' rights and civil rights victims' remedies, and upheld [the McCain-Feingold] campaign finance law." 

Thus, Professor Cole concludes that the legacy of the Rehnquist Court suffered in the end because, "since Bush v. Gore, many of the Court's most prominent and contentious cases have been decided by a majority comprised largely of liberal Justices, with one or more conservatives signing on to make up the majority."

Of course, Justice Sandra Day O'Connor was often the "conservative" swing justice who "sign[ed] on" with the four liberals -- Justices John Paul Stevens, David Souter, Ruth Bader Ginsburg and Stephen Breyer -- to form a High Court majority.  In fact, the positioning of Justice O'Connor at the center of and the deciding vote on virtually every constitutional controversy led to many commentators referring to the Court as the O'Connor Court.  For that reason, it was no surprise that conservatives were so excited -- and liberals so concerned -- at the possibility of President George W. Bush replacing Justice O'Connor with a more reliable conservative voice and vote on the High Court.

Up until last week, however, the Roberts Court --with Chief Justice Roberts replacing the late William Rehnquist and Justice Samuel Alito taking Justice O'Connor's old seat -- had not yet given conservatives a real reason to cheer their judicial confirmation victories.  Perhaps because the High Court had been so completely in transition, the decisions handed down this term had been relatively inconsequential and often congenial, even on the most contentious of issues.  That was, until last week.

Last Thursday, the five conservative justices seemed to announce for the first time that the Roberts Court had arrived to finish the conservative revolution begun by the Rehnquist Court.  In a landmark Fourth Amendment case, Hudson v. Michigan, the five conservatives led by Justice Antonin Scalia ruled that incriminating evidence need not be excluded from a criminal prosecution when the police, armed with a valid search warrant, failed to knock-and announce themselves before searching the suspect's house.

The "exclusionary rule," as it is called, has long been a thorn in the side of law enforcement -- and conservatives -- because it doesn't protect the innocent, but instead "perversely springs the guilty," explained Yale Law Professor Akhil Reed Amar.  Moreover, as Professor Amar noted after last week's decision, "no Founding Father ever called for a Fourth Amendment exclusionary rule, and no court in America ever followed such a rule in the entire century after the Declaration of Independence." 

In other words, the High Court's decision seemed to be an indication that, when the chips were down, these five conservative justices would hold the line and faithfully and carefully interpret the Constitution.

Or was it?

Less noticed at the time -- since he signed on to Justice Scalia's majority opinion almost in full -- was a concurrence by Justice Anthony Kennedy, which included the caveat that, in essence, told Court watchers not to read too much into the decision.  Justice Kennedy observed: "The Court's decision should not be interpreted as suggesting that violations of the requirement are trivial or beyond the law's concern.  Second, the continued operation of the exclusionary rule, as settled and defined by our precedents, is not in doubt."

That concurrence was just Justice Kennedy's first shot across the bow of the new conservative majority.  Four days later, on Monday, Justice Kennedy refused to join either the conservatives or the liberals in a highly technical but much-watched case about the reach of the federal Clean Water Act.  Though Justice Kennedy voted with the conservatives, he refused to sign on to their opinion (again authored by Justice Scalia).  Instead, in another concurrence that was as carefully positioned at the center of the Court as those of former Justice O'Connor, Justice Kennedy announced his own test for wetlands -- essentially deciding the issue on his own.

So after years of being the forgotten swing vote, in just the past week Justice Kennedy has announced himself as the new Justice O'Connor.  The question that remains is whether Justice Kennedy will more often follow the middle path he plotted in the High Court's recent Fourth Amendment decision or the Clean Water Act case.  His choice will be the difference between securing and continuing the principled conservative jurisprudence of the Rehnquist Court or the unprincipled split-the-difference jurisprudence of the O'Connor Court.