If U.S. Supreme Court Justice Clarence Thomas had his way, First Amendment protections for freedom of the press could be turned back not just to the pre-civil rights era but to the pre-Civil War era as well.

Let me explain. On Tuesday, Thomas wrote that the court ought to overturn its landmark 1964 New York Times v. Sullivan decision and allow the states free rein in deciding what standards should prevail in libel suits. In Sullivan, the court ruled that to prove libel public officials would have to show defamatory material about them was published with the knowledge that it was false or with reckless disregard as to whether it was true or false. That standard, known as “actual malice,” was later extended to public figures as well.

Now Thomas would reverse that. “The states are perfectly capable of striking an acceptable balance between encouraging robust public discourse and providing a meaningful remedy for reputational harm,” Thomas said. “We should reconsider our jurisprudence in this area.”

But the Sullivan decision was grounded in the failure of states to respect the right of the press to engage in “uninhibited, robust, and wide-open” debate, as the court put it, including “vehement, caustic, and sometimes unpleasantly sharp attacks on government and public officials.” The truth of the matter is that members of the white power structure in the South were seeking to weaponize libel laws in order to prevent the national press from reporting on its suppression of the civil rights movement. If the court hadn’t intervened, they would have gotten away with it.

The story of Times v. Sullivan is well told in Anthony Lewis’ book “Make No Law: The Sullivan Case and the First Amendment.” Supporters of the Rev. Martin Luther King Jr. took out a full-page ad in The New York Times in March 1960 titled “Heed Their Rising Voices.” The ad contained several minor errors of fact. For instance, it stated that King had been arrested seven times on trumped-up charges; in fact, he had only been arrested four times. It said that black students at Alabama State College in Montgomery, Alabama, had been padlocked into their dining room “in an attempt to starve them into submission” — a bit of hyperbole that was not literally true.

L.B. Sullivan, the Montgomery city commissioner in charge of the police, sued the Times for libel even though his name appeared nowhere in the ad. Sullivan won a three-day trial in Alabama state court that was rigged in his favor. For instance, the following year, on the 100th anniversary of the founding of the Confederacy, Sullivan staged a re-enactment of the swearing-in of Confederate president Jefferson Davis, with the same judge who had presided over his libel trial administering the oath of office.

It was against this deeply racist backdrop that the Supreme Court acted to end such abusive libel cases in 1964. The solution hit upon by Justice William Brennan, who wrote the decision, was to hold the press harmless for unintentional errors of fact. As Andrew Cohen wrote in The Atlantic upon the 50th anniversary of the case several years ago, “If there were no Sullivan, there likely would not have been a release of the Pentagon Papers or a rigorous investigation into Watergate or much of any withering criticism of government that appears today in any medium.” Or as Lewis himself put it in another of his books, “Freedom for the Thought That We Hate: A Biography of the First Amendment,” “New York Times v. Sullivan revolutionized the law of libel in the United States.”

My contention that Justice Thomas would bring us back to the pre-Civil War era is based on his apparent contempt for how the 14th Amendment was used to extend freedom of the press. The amendment, adopted in the immediate aftermath of the Civil War, forbids the states from trampling upon rights guaranteed by the U.S. Constitution. It took a while for the Supreme Court to rule that the First Amendment was among those rights. But in the case of Gitlow v. New York (1925), the court cited the 14th Amendment in extending its jurisdiction for the first time over state laws regulating speech.

No matter that Benjamin Gitlow, the hapless communist who’d been convicted of violating New York’s criminal syndicalism law for publishing a turgid left-wing manifesto, was sent to prison anyway. By recognizing that “freedom of speech and of the press" are protected "from impairment by the States," the court transformed “Congress shall make no law … abridging the freedom of speech, or of the press” into a guarantee pertaining to state and local government as well.

Thus Justice Thomas demonstrates not only ahistorical disdain for the role that combatting racism played in the Sullivan decision but also for the long-settled principle that state and local governments may not take away protections guaranteed by the Constitution. In his opinion this week, Thomas pays lip service to the 14th Amendment. But it’s hard to square that with his enthusiasm for turning over basic press protections to the tender mercies of the states.

Fortunately Thomas seems likely to find himself alone on this. President Trump, as we know, has spoken of his desire to “open up our libel laws.” But Adam Liptak, who covers legal affairs for the Times, wrote on Tuesday that both of Trump’s appointees, Justices Neil Gorsuch and Brett Kavanaugh, have spoken approvingly of Times v. Sullivan. The decision appears to be safe — at least for now.

Still, Thomas’ out-of-the-blue opinion — expressed in a decision about a libel suit involving Bill Cosby, of all things — shows that the battle for free speech is never completely won. Rather, it has to be fought, over and over again.

WGBH News contributor Dan Kennedy’s blog, Media Nation, is online at dankennedy.net .