The National Memorial for Peace and Justice in Montgomery, Alabama opened with a mix of applause and catcalls. The applause was for recognition of arguably the most hideous, heinous and barbaric assault on black rights in the form of thousands of documented lynchings of black men and women. There are many gruesome pictures on display of black men and women being burned, dragged in chains, roasted alive and dismembered while whites crack jokes and mug for the cameras. According to NAACP figures, between 1890 and 1960, 5,200 blacks were burned, shot or mutilated by lynch mobs. The horrid death toll is almost certainly higher, since in many cases sheriffs and local officials failed to deem the murders significant enough to report.

Still, there were criticisms about depicting any of this. “Why bring up all this old gruesome stuff again? It was decades ago, so, it’s time to get over it and move on,” they said.

This complaint should be ignored for three compelling reasons.

The first is that history — the good and the bad — can’t simply be airbrushed away. History provides a teaching moment and a learning experience for generations to learn from, if for nothing else than to not make the mistakes of the past.

The second is that few exhibit such public fervor for remembering the past as Jews and Armenians who have institutionalized their respective Holocaust and Genocide experiences as teaching and learning moments.

The third and most disturbing reason is lynchings were not just murderous assaults on blacks by primitive townspeople in backwater Southern towns. This was a national assault that took place in many locales outside the South, egged on by prominent people and officials and then ignored and tacitly protected by the federal government.

Most lynch murderers made no attempt to hide their acts. Some took out ads in newspapers and circulated flyers announcing lynchings. They ignored the 1908 ban by the US Postal Service on sending violent material in the mail and conducted a brisk trade in souvenir postcards and letters with snapshots of lynched victims.

The NAACP relentlessly lobbied Congress and the White House to pass an anti-lynching law, but the civil rights group was ignored.

Every president from Theodore Roosevelt to John F. Kennedy refused to draft or vigorously support a federal law to end lynching. FBI Director J. Edgar Hoover successfully manipulated Presidents Franklin Roosevelt through Kennedy to steer the FBI away from direct investigation of lynchings.

Presidents, attorneys general and federal officials said their hands were tied, because it was the job of the states to prosecute lynch murderers. But the states refused. Fewer than 1 percent of the murderers were ever tried in state courts. Rather than risk alienating politically powerful Southern state officials and jeopardizing votes, the feds rationalized their hands-off policy toward lynching with a narrow and rigid interpretation of the federalist doctrine of separation of state and federal power.

This was a face-saving political cop-out. In many cases, a bevy of Southern sheriffs, mayors and municipal and state officials openly aided and abetted lynch mobs. The Justice Department had two powerful legal statutes to go after them. The statutes authorized prosecutions of public officials and law enforcement officers who, acting under color of law, committed or conspired with others to commit acts of racial violence. They were based on the 14th Amendment’s due process and equal protection clause.

The hideous legacy of the near-century-long federal hands-off policy toward lynching is hardly an academic, by-gone remnant of the past. The absolute refusal of Attorney General Jeff  Sessions and the Justice Department to vigorously prosecute racially motivated hate crimes, let alone police violence against blacks and Latinos, is a modern-day carryover of the official blind eye to black lives. The police shootings of unarmed blacks with almost no punishment for the cops who wantonly kill have often been compared to the old lynch mentality.

The Lynching Memorial graphically exposes the shame and disgrace of lynching. The tragedy is that American presidents and the Congress never shared that horror. Until federal officials publicly admit their complicity in lynch violence, it will remain the federal government’s dirtiest racial secret.