Americans have witnessed so many tragedies that we have become numb — or so it seems — to their effects.

Politicians get assassinated. Buildings are blown up. Madmen open fire in schools, churches and movie theaters. And, yes, police officers kill citizens in acts of brutality.

However, this latest tragic event — the death of George Floyd more than a week ago on a Minneapolis street — seems sadly different. This one well might stick in our national consciousness for far longer than anything else we had have witnessed.

Why is that?

I want to posit a couple of theories.

One is the physical evidence we all have seen of a cop holding Floyd to the ground, with his knee pressing against the man’s neck. We watch the cop do nothing to respond to Floyd’s pleas for help, his cries for his mother, his crying out that “I can’t breathe.” The cop, Derek Chauvin, hold him down — while the suspect is handcuffed. Floyd loses consciousness. Chauvin still doesn’t lift his knee off of Floyd’s neck.

How in the name of human decency does one explain this away? How will this former police officer tell the world why he held down a man who offered no resistance until he no longer has a pulse? You’ve seen the video, yes? He looks at the young bystander who took the video as if to say, “So what are you looking at?”

This event calls out loudly and clearly to the issue of how police treat African-American men and whether they treat them differently than they do, say, white men or white women.

The second notion that might produce the seminal moment in police-black community relations has been the reaction of police agencies around the country. We are hearing other law enforcement officials condemning the actions of Derek Chauvin. They are standing — and kneeling — with peaceful protesters in cities from coast to coast to coast in solidarity with the concerns they are raising.

So, the dialogue has commenced. Americans are demanding justice be delivered to Chauvin and the three police colleagues who watched him kill George Floyd. They also are demanding that police cease demonizing American citizens simply because of their skin color.

This outrage should last for as long as it takes for there to be tangible evidence that we are slaying this deadly beast.