Dallas Police Chief David Brown at a prayer vigil after five officers were killed and seven were injured in a coordinated ambush at a protest against police brutality. (Spencer Platt/Getty Images)

It was almost a generation ago when Rodney King, the black victim of a vicious beating by white Los Angeles police officers, issued his plaintive call: “Can we all get along?”

Rick Zamarripa echoed that 24 years later after his son Patrick was one of five Dallas police officers killed by a black man. “I wish everybody could just get along,” the father told CBS News.

Thursday’s assault by Micah Johnson on Dallas police — President Obama called the shootings “a vicious, calculated and despicable attack on law enforcement” — was said to be a retaliatory strike that quickly followed back-to-back point-blank police killings of black men, Alton Sterling in Baton Rouge and Philando Castile in Falcon Heights, Minn.

Obama also called Johnson “demented.” Yet, the gunman’s actions also reflect the explosive, deep-seated anger felt by black Americans who would never take their outrage that far.

Last week’s killings filled the nation with horror and anxiety and left other countries confused and fearful about our violence. The Bahamas, which is 90 percent black, warned its young men traveling to the United States “to exercise extreme caution in affected cities in their interactions with the police.”

“Black lives matter” is a fact and an aspiration. Given history and a broad range of conditions in this country, “black lives are cheap” seems more accurate. Blue lives also were cheap to Johnson.

Relations between police and black America have always been weak at the seams. Now, the killings in Texas, Louisiana and Minnesota have exposed the big hole in the country’s multicultural quilt.

“There’s not a black America and white America and Latino America and Asian America — there’s the United States of America,” Obama, then a Senate candidate from Illinois, said at the Democratic convention in 2004.

On Saturday, his tone reflected what is, instead of what should be.

“So there is sorrow, there is anger, there is confusion about next steps,” he said from the NATO Summit in Warsaw.  “But there’s unity in recognizing that this is not how we want our communities to operate.  This is not who we want to be as Americans.”

Yet this is who we are. This is how our communities operate. Not in totality, but enough to make us shudder at how violent America is.

Like the biddings of King and Zamarripa, Obama’s 2004 remarks were more hopeful than real. It’s going to take more than Kumbaya talk to heal relations between the police and the African American community.

Particularly now.

For Rep. Eddie Bernice Johnson (D-Tex.), who lives just blocks from the scene of the Dallas shootings, the American mosaic has become more ragged since Obama was elected president in 2008.

“Race relations have deteriorated greatly in the last five to eight years,” Johnson said in an interview. “It’s the reality. It’s no point in denying it. We’ve got to do better. … The hostility we feel even in the body we serve in is indicative of negative race relations. We can’t ignore it and we can’t deny it and think it’s going to go away.”

The reason for this trend?

“I can tell you what the average black American thinks,” she said. “They think that because our president is African American that the white racism has been rebirthed.”

Racism isn’t always overt, as it was in Charleston, S.C., last year when Dylan Roof, who had previously posed with a Confederate battle flag, allegedly opened fire and killed nine black worshippers at Emanuel African Methodist Episcopal Church. Implicit bias isn’t as deadly, but it can be more insidious.

Attorney General Loretta E. Lynch announced last month that all Justice Department law enforcement officers and prosecutors will take training in implicit bias. The department defined implicit bias as “the unconscious or subtle associations that individuals make between groups of people and stereotypes about those groups.”

In a memo to staffers, Deputy Attorney General Sally Yates said implicit bias “presents unique challenges to effective law enforcement, because it can alter where investigators and prosecutors look for evidence and how they analyze it … these trainings reaffirm our commitment to a criminal justice system that is fair, impartial, and procedurally just.”

That’s a start.

So was the report by the President’s Task Force on 21st Century Policing, published last year. The first of its six recommendations is building trust “on both sides of the police/citizen divide.”

Toward that end, Obama said he is calling law enforcement officials, community activists and civil rights leaders to the White House this week, when he also plans to visit Dallas, “to start moving on constructive actions that are actually going to make a difference.”

Another aspirational statement. At the moment, it’s hard to be optimistic.