Bill Clinton trespassed against the cardinal rule of contemporary Democratic politics, which is that Thou Shalt Not Contradict Black Lives Matter Protesters.

Clinton’s lapse came at a Philadelphia rally last week. When demonstrators inveighed against the 1994 crime bill signed by Clinton, the former president gave much better than he got. He rebutted them in finger-wagging detail, repeatedly returning to the point that the crime bill sought to diminish the rampant criminality that was destroying black lives.

Clinton thought he was winning the argument, and by any reasonable standard he was — but, politically, he committed a multitude of sins.

He defended the old term “super predator” as an accurate description of gang leaders who prey on kids — not realizing that the phrase has been deemed dehumanizing (gang leaders are very sensitive to such microaggressions). Instead of denouncing the police as agents of systemic racism, he defended sending more of them into the streets. And by using the phrase “black lives” in the context of blacks killing other blacks, he signaled he doesn’t get that the only approved use of the slogan is as a bludgeon against the criminal-justice system.

In short, Clinton demonstrated a common-sensical, pre-Black Lives Matter understanding of criminal justice, and quickly had to backtrack. Presumably, he won’t be guilty of such an offense ever again.

Both Clinton and his critics exaggerate the effect of the 1994 crime bill, which, among other things, funded more cops and prisons. Clinton attributes the drastic decline in crime rates to it, when the drop had already begun. The critics attribute the drastic increase in incarceration to it, when that, too, preceded the bill.

But the notion that the crime bill, and other tough-on-crime measures like it, was part of a racist dragnet to imprison black men guilty of low-level drug offenses is obviously absurd.

It is easy to forget now, but between 1960 and 1990, the United States experienced perhaps the worst crime wave in its history. Violent crime increased more than 350 percent. Across the 1960s, robbery rose 500 percent in cities with a population of a million. It would be impossible for the political system not to respond vigorously to such a tide of disorder, especially when the criminal-justice system was initially so inadequate to the task.

In his book “The Rise and Fall of Violent Crime in America,” Barry Latzer notes how the criminal-justice system was fraying as crime spiked in the late 1960s: “The number of arrests per reported crime went down, not up; sentencing to prison occurred less often, not more; and prison time served for serious crimes actually shortened, not lengthened.”

Subsequently, we readjusted, and it wasn’t an exercise in quasi-white supremacy. From 1976 to 2005, blacks were 47 percent of murder victims. Bill Clinton’s talk of kids wasn’t just pulling at the heartstrings. During the crack epidemic in Washington, D.C., about 500 kids were shot and stabbed in a roughly two-year period. Since their communities suffered so grievously from drug crime, black Democrats supported important legislative elements of the crackdown on drug offenses from the 1970s onward.

Yet the war on drugs wasn’t the main driver of the remarkable 30-year rise in incarceration, from roughly 300,000 to more than 1.6 million. According to John Pfaff of Fordham Law School, less than 20 percent of the inmates in state prisons (they house most U.S. prisoners) are there primarily on drug charges. The vast majority are guilty of violent or property offenses.

There is no doubt that policing and prisons — as well as the waning of the crack epidemic — played a role in breaking the great crime wave of the 1960s. That we are safer creates the political opening to rethink our incarceration policies. Bill Clinton will now want to button his lip before saying such a thing, but it doesn’t make it any less true.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.