Left-wing terrorism has been a hush-hush topic throughout modern American history.

From the 1880s through the 1920s, anarchist terrorism, often associated with immigrants, claimed hundreds of lives between shootings and bombings, including President William McKinley, numerous lesser politicians, and even an unsolved bombing of Wall Street, which killed over 30 and wounded hundreds. History repeated in the 1960s with another American left-wing terror wave, borne of anti-Vietnam War protests, which targeted military and federal facilities nationwide, dragging painfully into the 1980s. Their last big attack was bombing Congress in 1983, which miraculously killed no one.

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Liberals conveniently memory-hole this long history of domestic terrorism, preferring to blame shadowy, often imaginary far-rightists for all extremist violence. This ideological amnesia has real-world consequences, especially since Democrats don’t recognize the domestic terrorism they’re flirting with by encouraging attacks on federal officials, particularly Immigration and Customs Enforcement.

Condemnation of ICE employees as criminals and “fascists” has become so routine now, even among top Democrats who ought to know better, that there’s a climate of violence lingering over the Trump administration’s efforts to enforce immigration law. Left-wing activists repeatedly threatened ICE employees in Los Angeles, many of them associated with antifa, so that National Guard and federal troops were mobilized to protect them from the mob.

Violence and harassment against ICE employees has risen 700% since the beginning of this year, according to the Department of Homeland Security, while left-wing activists have gone online to “doxx” ICE officials and even their families, revealing their names and residences, which exposing them to violence, not to mention intimidation right at home.

Most seriously, a dozen well-equipped extremists attacked an ICE detention facility in Alvarado, Texas, on July 4, firing dozens of rounds at law enforcement. A local officer was shot in the neck during the attack. Federal authorities have arrested 10 of the attackers, while the search continues for others, including 32-year-old Benjamin Song, a former U.S. Marine Reserve member, for firing two AR-15 style assault rifles at ICE and police.

The Alvarado attack was planned and prepared by domestic terrorists seeking to block ICE from performing its legally mandated mission. This is a new wave of domestic terrorism in the making, and Democrats have been slower to condemn this ominous violence than they ought to.

Liberals must recognize that they possess a radical Left fringe which embraces, or at least condones, violence against anyone they deem to be “fascists” (which now seems to be most Republicans). Before Barack Obama took over the party, Democrats commonly understood that they had to keep their radicals in check; no longer. Dispense with the shopworn nonsense that antifa doesn’t exist, or is so nebulous as not to matter. Anarchists were a decentralized bunch, too, by design, yet that loose structure didn’t prevent their pervasive terrorism. To the contrary.

The country is at a hinge point where, if Democrats don’t unambiguously condemn left-wing extremism and violence, soon, we seem sure to get more of it. Casual talk extolling violence against ICE or other federal agencies in the name of “resisting” Trump will get people killed, so cut it out.

While organized domestic terrorism constitutes a serious threat, individuals acting out their left-wing fantasies represent real danger too. Misfits radicalized by a witches’ brew of extremism, one part Free Palestine, one part migrant activism, one part LGBT, plus a good deal of inchoate rage, sometimes kill people. Two months ago, Elias Rodriguez, a radical leftist, gunned down two Israeli Embassy employees in cold blood in downtown Washington, DC, to support Gaza, or so he claimed. Anarchists would recognize such murders as “the propaganda of the deed.”

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Some of this radicalism is difficult for others to decipher. As many as six killings, including the shooting death of a U.S. Border Patrol agent in Vermont in January of this year, can be attributed to a bizarre cult called the Zizians, after their leader, Jack “Ziz” LaSota. The Zizians grew out of an obsession with transhumanism, transgenderism, and artificial intelligence, then graduated to murder. A recent profile by the New York Times detailed how the Zizians went badly wrong, without dwelling on the presence of terrorists reminiscent of the Manson Family on the radical fringe of the transgender movement.

The third wave of American domestic left-wing terrorism is rising and will land with destructive force in this decade unless it’s halted without delay. Law enforcement has a part to play there, but the main task falls to Democrats who must resolutely condemn and separate themselves from anyone seeking to change politics through violence. Stopping terrorists “left of boom,” as the pros say, is imperative. The clock’s ticking.

John R. Schindler served with the National Security Agency as a senior intelligence analyst and counterintelligence officer.