Almost a quarter of the U.S. Congress, along with President George W. Bush and President Obama, will be in Selma, Ala., Saturday for the 50th anniversary of the civil rights march that led to the 1965 voting rights act.

I’ve found myself quietly crying in a Selma church, filled with pride in our nation as the home of brave people of all colors and faiths willing to sacrifice in every generation for the American ideal of equality.

At a time of polarized politics in Washington, this celebration is a moment of political unity. It brings people together; it crosses racial and political lines, as evidenced by the presence of President Bush and more than 20 Republican members of Congress.

I’ve found myself quietly crying in a Selma church, filled with pride in our nation as the home of brave people of all colors and faiths willing to sacrifice in every generation for the American ideal of equality.

As the author of “Eyes on the Prize – America’s Civil Rights Years,” and as someone who has gone on one of the annual congressional pilgrimages to Selma, I can tell you it is an amazing experience. Walking those small-town Southern streets raises American history beyond even the best writing and films. I’ve found myself quietly crying in a Selma church, filled with pride in our nation as the home of brave people of all colors and faiths willing to sacrifice in every generation for the American ideal of equality.

That inspiration is needed now as America faces another critical racial test: improving how the police deal with black people. Much of the current angry reality of black tension with police is a troubling reflection of what happened in Selma 50 years ago.

The white state troopers who beat the black people marching for their right to vote remain a big part of the reason black Americans have never seen the police as a group dedicated to serve and protect them.

The events in Selma fit with New York Police Commissioner Bill Bratton’s recent statement on current relations between blacks and police: “Many of the worst parts of black history would have been impossible without police.”

This week the Justice Department reported that police in Ferguson, Mo. regularly stopped black drivers, jaywalkers and others with little cause except for the purpose of collecting fines for city of Ferguson's treasury.

From the start of the Selma protests for black voting rights, police were used to halt the movement. Before Dr. Martin Luther King Jr. and other civil rights activists arrived in Selma in January 1965, the local police had already arrested and beaten black people simply for attending clinics on how to register to vote.

Dr. King’s plan was to use news and pictures of the police violence against people standing up for voting rights to force Congress to enact federal laws to better protect voting rights for blacks.

In the words of Andrew Young, one of Dr. King’s top aides, “We [wanted] to establish in the mind of the nation that a lot of people who want to register are prevented from doing so.”

Police violence against blacks was a fact of life in Selma. The sheriff, Jim Clark, shoved down and arrested a middle-class and middle-aged black woman, Amelia Boynton, who was standing in line to register; Clark later elbowed another marcher, and when she fought back, he had his men hold her down while he hit her in the head with a stick.

“If Negroes could vote, there would be no Jim Clarks,” King told activists in Selma. “Our children would not be crippled by segregated schools …”

Later, C.T. Vivian, executive director of Dr. King’s group, the Southern Christian Leadership Conference, stood before police blocking the door to the registrar’s office and said, “We know your badge numbers … There are those who followed Hitler like you blindly follow this Sheriff Clark … You can’t keep anyone in the U.S. from voting without hurting the rights of all other citizens. Democracy is built on this. This why every man has the right to vote…”

Clark responded by hitting Vivian in the mouth, even as television cameras captured the bloody scene.

Meanwhile, only 1 percent of blacks in Selma had been allowed to register to vote. As a 65-year-old black man famously said at the time: “If what I done ain’t enough to be a registered voter with all the taxes I got to pay, then Lord have mercy on America.”

That led to the events at the Pettus Bridge on March 7. Dr. King was not there, but John Lewis, then head of the Student Non-Violent Coordinating Committee and now a congressman from Georgia, led activists to start a march from Selma across the bridge and down the highway to the state capital, Montgomery, to call for voting rights. Alabama state troopers ordered them to disperse, and then they suddenly rushed into the marchers, knocking them down and beating them. Some of the marchers were trampled by horses.

It is that painful history that FBI director James Comey touched on recently when he spoke of the antipathy that still exists between black Americans and the police.

“At many points in American history, law enforcement enforced the status quo, a status quo that is often brutally unfair to disfavored groups,” the FBI chief said. Comey keeps a copy of the approval for an FBI wiretap on Dr. King on his desk as a reminder of how law enforcement can be turned into a tool of oppression.

Fifty years after Selma we live in an America where even Jesse Jackson confesses to being nervous when he sees young black men walking behind him. Grand juries, made up of everyday people of all races, make their anxiety about black crime clear when they regularly give every benefit of the doubt to police, even when police bullets and chokeholds kill unarmed black men.

And then there is the failure of black American leadership to come to terms with lawless, even violent behavior by young black men. There are no civil rights marches calling on black people to do something about the fact that about half of the nation’s murder victims are black, and that most are between the ages of 17 and 29. Where are today’s marches against family breakdown and bad schools with high minority dropout rates that lead to high unemployment, poverty and crime rates?

Too often activists are still directing their anger at the state police on the Pettus Bridge instead of looking at problems in their own ranks. 

This weekend’s celebration is a time to remember history, to be inspired and reminded that America, black and white, citizen and policeman, is capable of the unity and principled action needed to make new history.

Juan Williams is a co-host of FNC's "The Five," where he is one of seven rotating Fox personalities.