As a practical matter, the death penalty has been all but abolished in the United States.

Although homicides have spiked in recent years — nearly 23,000 Americans were killed in 2021, a number not seen since the early 1990s — the number of killers annually executed for murder has dwindled to fewer than 20. Last year, only 18 murderers were put to death. On the front page of its extensive website, the Death Penalty Information Center reports that executions in the United States have declined by 82 percent since 1999. Over the same period, death sentences have dropped more than 90 percent.

The decades-long campaign to eliminate capital punishment as a legal option has been remarkably successful. Only 24 states now retain the death penalty on their books. In 23 states (and Washington, D.C.), it has been abolished outright. In three other states, executions have been banned through the imposition of an indefinite moratorium by the governor.

To be sure, polls consistently show that a majority of Americans are in favor of the death penalty for murderers. But when respondents are asked to choose between the death penalty and life in prison without parole, a majority now says that life without parole is preferable. Indeed, anti-death penalty campaigners have long argued that no-parole life sentences make executions unnecessary. To permanently incapacitate the most dangerous killers, they have frequently insisted, society doesn’t have to put them to death — it can keep them behind bars instead.

To be clear, I have never agreed that life without parole is an adequate substitute for capital punishment. In my view, there are times when justice requires nothing less than the death penalty. Nevertheless, I can’t deny that death-penalty abolitionists have been extremely successful at promoting life without parole as an alternative to executions. Most of the states that have abolished the death penalty in recent years, including New Mexico, Illinois, Connecticut, Maryland, New Hampshire, Colorado, and Virginia, have expressly replaced it with life sentences that are ineligible for parole.

Guess what the activists want to get rid of next.

“As part of a slate of legislation targeting criminal justice reform,” the Globe reported on July 28, “state lawmakers are pushing to end the practice of sentencing people to life in prison without the possibility of parole.” Under a bill introduced by two Boston Democrats, Senator Liz Miranda and Representative Christopher Worrell, there would no longer be any way to guarantee that a convicted murderer — not even the most merciless terrorist or serial killer — would go to prison for life. Every inmate would eventually be able to seek parole. Miranda and Worrell want justice for the victims to be discounted so that killers who have been “rehabilitated” can be rewarded.

At a State House hearing, witnesses trotted out a slew of predictable arguments. They claimed that there are too many people in prison, that locking criminals up for life is expensive, that many convicts are no longer a danger to society, that older prisoners have health problems. But no one acknowledged the implicit bait and switch: In Massachusetts, as in many other states, the elimination of the death penalty was conditioned on the assurance that convicted first-degree murderers would never go free. Now, with the death penalty eliminated in most places, that assurance is under attack.

“When we outlawed the death penalty in Massachusetts, life in prison without any possibility of a parole review should not have taken its place,” Miranda said.

She quickly added a caveat: “No one here advocates the release of serial killers and other worst-of-the-worst offenders.”

That’s what she says now. What will she say once life without parole is outlawed?

Some progressive activists are open about their ultimate goal — the abolition not just of the death penalty or life sentences but of all imprisonment. They know that cannot be achieved at once, so their strategy is to trim what they call the “carceral state” one salami slice at a time.

“We know we won’t bulldoze prisons and jails tomorrow,” acknowledge Ruth Wilson Gilmore and James Kilgore in “The Case for Abolition” at The Marshall Project, a news organization focused on criminal justice issues. “We’re in a long game.”

David Stein, a professor at the University of California, Santa Barbara, embraces a similar step-by-step strategy. “Abolitionists have worked to end solitary confinement and the death penalty, stop the construction of new prisons, eradicate cash bail, organized to free people from prison, [and] opposed the expansion of punishment through hate crime laws and surveillance,” he writes in the left-wing journal Jacobin. Most Americans would regard doing away with imprisonment as outlandish, but US history offers plenty of examples of sweeping social innovations — from independence to women’s suffrage to same-sex marriage — that also seemed unthinkable at first.

The bill just introduced on Beacon Hill isn’t the first legislative attempt to eliminate sentences of life without parole. If it doesn’t pass this year, it won’t be the last attempt. For years, advocates told voters that life imprisonment was a merciful alternative to the death penalty. Now they insist that life without parole is inhumane too. Progressive true believers got rid of capital punishment, but their war to abolish punishment itself still has a ways to go.