The news from the March 2 oral argument in the Supreme Court’s biggest pending case was that the five conservative justices seem poised to make the Second Amendment right to bear arms applicable to state and local gun controls, as well as federal. In the process, they will strike down the unusually strict handgun bans in Chicago and Oak Park, Ill. — probably in June.

But debate about the gun case, McDonald v. City of Chicago, has ranged far beyond guns. It has spawned an alliance of convenience among distinguished scholars in the progressive and conservative-libertarian camps.

Both have filed amicus briefs that take the gun-rights side while mainly seeking to expand other rights as well.

The detailed constitutional arguments show with unusual clarity why efforts to expand rights — whether favored by conservatives or liberals, or both — typically boil down to a bare-majority judicial faction using highly debatable theories to override democratic governance.

Many of the briefs in the gun case urge the Court to revive the 14th Amendment’s open-ended but long-moribund "privileges or immunities" clause and use it as a new fount of judicial power to strike down enactments imposed by majority rule. But the privileges-or-immunities alliance breaks down when its members are pressed on which laws should be struck down and which rights should be expanded or created.

Conservative libertarians who want the courts to reject economic regulations stress the considerable evidence that the authors of the privileges or immunities clause wanted to protect property and contract rights as well as gun rights.

Progressive scholars, on the other hand, see the same principles evolving over 142 years to mandate judicial protection of welfare rights — called "the new property" by some — as well as privacy, abortion, gay rights, assisted suicide, and other liberal favorites about which nobody was thinking when the 14th Amendment was adopted in 1868.

Both groups are armed with powerful historical evidence that the 1873 precedent that gutted the privileges or immunities clause, the Slaughterhouse Cases, misread the intent of the amendment’s framers. The precedent also paved the way for subsequent decisions that helped Southern whites subjugate freed slaves by, among other things, disarming them and leaving them defenseless against the Ku Klux Klan.

But the justices who spoke during the oral argument on McDonald — including those pushing to expand gun rights — were hostile to the privileges-or-immunities justification. Justice Antonin Scalia deprecated the clause as "the darling of the professoriate."

Why so dismissive?

Were the justices showing respect for a deeply rooted, 137-year-old precedent, as several argued? Well, sure. They always show respect for precedent — except when they don’t.

Were they showing judicial restraint, by passing up a chance to grab more power? Doubtful. None of the nine justices has shown much modesty in finding support for his or her own policy preferences in the Constitution.

Were they worried about what their ideological adversaries (and future adversaries) might do with an open-ended license to conjure up new "privileges or immunities" by refracting selected fragments of historical evidence through their own philosophies?

That’s my guess. The justices know that whatever clarity the text of this and other constitutional clauses may have once had has receded over many decades, as the clarity of a road sign recedes in the rearview mirror. They also know that the future content of a revived privileges or immunities clause would likely hinge on nothing more objective than the ideological leanings and policy preferences of future justices and the presidents who pick them.

You want the Court to comb through 19th-century history and find a mandate for unfettered capitalism? Vote Republican. You want it to impose welfare rights, with a heavy dose of judicial empathy? Vote Democratic. And hope for well-timed vacancies and long-lived justices who share your policy preferences.

Scalia, the great originalist, suggested that ancient and deeply rooted precedents trump original meaning.

Meanwhile, the notion of constitutional rights as immutable principles protecting our liberties from majoritarian tyranny morphs into rule by whichever faction happens to have a one-vote majority on the Supreme Court.

Shifting majorities have long advanced their own views incrementally by reading ambiguous historical evidence as supporting causes ranging from gun rights to gay rights, both of which have been put over the top by Justice Anthony Kennedy’s conservative leanings on the former and liberal leanings on the latter.

But none of the nine — except perhaps Justice Clarence Thomas, who was silent as usual during the argument in the gun case — seems prepared to risk giving a privileges-or-immunities blank check to whichever faction may control the Court in the future.

Some history: The 14th Amendment was adopted in 1868, after many months of congressional hearings, primarily to give freed slaves the rights of full citizens and give Congress the power to override oppressive state and local laws, especially in the South.

Here’s the critical language for purposes of the current debate: "No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; … "

Historical evidence strongly suggests that the first clause was intended to make applicable against the states and their localities all provisions of the first 10 amendments (the Bill of Rights) — which had previously limited only the federal government — and perhaps also an unspecified number of other, unenumerated rights.

But the Supreme Court virtually nullified this broad language in the 1873 Slaughterhouse Cases by narrowing it to a few "privileges" and "immunities" rooted in federal citizenship, such as the right to be protected while at sea.

Subsequent decisions using similar logic helped facilitate the subjugation of blacks in the South for most of the next century. These rulings also help explain why most of the Bill of Rights, including the First Amendment, was not applied to state or local governments until the 1920s and thereafter.

By then, the Supreme Court had found another way to apply provisions of the Bill of Rights — almost all of them, eventually — against the states, along with other judicially recognized (or, critics say, judicially invented) rights including family privacy, contraception, and abortion. The Court construed the 14th Amendment’s due process clause as "selectively incorporating" against the states those rights that the justices deemed fundamental to American liberty.

This "substantive due process" doctrine has been assailed by many conservative critics — especially since Roe v. Wade — and some liberals as a judicial power grab inconsistent with the language of the due process clause, which by its terms guarantees only procedural fairness.

But advocates of expansive judicial power to create new rights — liberals and conservative libertarians alike — have responded with strong evidence that the long-buried privileges or immunities clause was originally understood to give courts even broader powers than the due process clause.

Despite this evidence, Scalia, the great originalist, suggested that ancient and deeply rooted precedents trump original meaning. "Even I have acquiesced" in the legitimacy of substantive due process, he said, even though "I think it’s wrong."

A deeper question, in my view, is this: Why should the words of a few congressional leaders more than 140 years ago — as seen through the diverse, distorting lenses of current Supreme Court majorities — trump the views of elected majorities today?

As Justice Stephen Breyer asked, why should equivocal evidence of what was intended in 1868 wipe out a handgun ban thought by Chicago’s elected leaders to have saved hundreds of 21st-century lives?

These fundamental questions about the 14th Amendment have come to the fore because of a big 5-4 decision in 2008. The Court held for the first time that the Second Amendment protects a right to "keep and bear arms" not only for service in now-defunct state militias — as had long been widely assumed — but also for self-defense against intruders and other, so-far-unspecified, individual uses.

The 2008 decision struck down the District of Columbia’s broad handgun ban, while noting that other gun controls imposed by the federal government and its enclaves would be upheld if deemed reasonable by the courts. It left open the question before the Court now: Did the 14th Amendment make the same (or similar) gun rights applicable against state and local regulation?

I could see no clear winner in the 2008 decision’s learned but clashing interpretations of the Second Amendment. "It seems almost perverse," I wrote then, "to be assessing what gun controls to allow based not on examining how best to save lives but on seeking to read the minds of the men who ratified the Bill of Rights well over 200 years ago."

It’s almost as hard to read the minds of those who wrote the 14th Amendment 142 years ago. They do seem to have intended to protect the rights of freed slaves and others to have guns to defend themselves against KKK terror. But the rest, or most of it, is in the eye of the beholder.

This article appeared in the Saturday, March 6, 2010 edition of National Journal.