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DALLAS – President Barack Obama on Tuesday gathered with politicians, police officers and families of the fallen in Dallas to call for unity in the wake of a shocking slaying of five police officers by a black man who said he wanted revenge for the killings of blacks by police.

Speaking at the memorial, President Obama said the shootings of five Dallas police officers would appear to have exposed the “the deepest fault line of our democracy” but that Americans must reject such despair.

He asked Americans to find the character to open “our hearts to each other” and asked whether Americans can see in themselves a common humanity and recognize how different experiences have shaped people’s perceptions.

WATCH: Obama to make all-too-familiar tribute during Dallas memorial visit. Aarti Pole reports.

4:06 Obama to make all-too-familiar tribute during Dallas memorial visit Obama to make all-too-familiar tribute during Dallas memorial visit

Obama said, at times, he has doubts, saying “I’ve been to too many of these things.” He added that’s why Americans should pray for each other to have not a heart of stone but one that’s open to the fears and challenges of their fellow citizens.

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Obama also says he believes the police officers who died in Dallas did not die in vain, and he says there is evil in the world, which is why “we need police departments.”

WATCH: Obama says America should not be scared of Black Lives Matter movement

1:44 Obama: America should not be scared of Black Lives Matter movement Obama: America should not be scared of Black Lives Matter movement

However, he also said Americans can’t dismiss protesters who call attention to racial issues 50 years after the Civil Rights Act was passed, as troublemakers.

Obama said Americans know that bigotry remains, some are affected by it more than others and that none of us “are entirely innocent.”

He also said that the country asks police “to do too much” and that we do “too little ourselves.”

“The soul of our city was pierced,” Dallas Mayor Mike Rawlings said, as he welcomed Obama to a memorial service. The group had assembled because to combat “a common disease” of violence and honour those who fight it, “our men and women in blue, our peacemakers in blue.”

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Rawlings spoke steps from five empty chairs and five portraits of the dead officers.

READ MORE: #BlackLivesMatter: How to talk to your kids about racism

Dallas police chief Chief David Brown recited lyrics from Stevie Wonder’s song “As” to the families of the five officers who were fatally shot last week.

Brown said he often would find himself at a loss for words as a young man trying to get dates, and would use lyrics to express himself.

That’s what he did at the service for the families of those who died. “I’ll be loving you until the rainbow burns the stars out of the sky, until the ocean covers every mountain high,” he said, receiving a long, loud standing ovation from those in attendance.

A call for national and solidarity was reinforced by several speakers at the interfaith service, including former President George W. Bush, a Dallas resident, who attended with his wife, Laura.

“At times it feels like the forces pulling us apart are stronger than the forces binding us together,” Bush said. “Too often we judge other groups by their worst examples, while judging ourselves by our best intentions. And this has strained our bonds of understanding and common purpose.”

Bush called on Americans to reject the unity of grief and fear.

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“We want the unity of hope, affection and higher purpose,” he said.

VIDEO: Hundreds gather for candle light vigil in Dallas

1:34 Obama to address memorial service for 5 fallen officers killed in Dallas shooting Obama to address memorial service for 5 fallen officers killed in Dallas shooting

Obama has denounced the shooting as a “vicious, calculated and despicable attack on law enforcement” by a “demented” individual. And he has argued that, despite the heated public outcry of the past week, the country is not as divided as it may seem.

Obama planned to return to that message in his speech Tuesday and his choice of travelling companions underscored the theme. Republican Sen. Ted Cruz of Texas and House Democratic Leader Nancy Pelosi of California both joined Obama on Air Force One for the flight to Dallas. Republican Sen. John Cornyn, attended and spoke at the service, but did not travel with the president.

He described the attack as deeply personal.

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“Being a Texan doesn’t describe where you’re from it, describe who your family is,” the senator said.

READ MORE: ‘This killing, it has to stop’: Dallas doctor tears up talking about recent shootings

The White House said president worked late into the night writing his speech and consulting scripture for inspiration.

Just a few weeks ago, Obama spent hours in Orlando, Florida, consoling the loved ones of 49 people who were killed in a shooting rampage at a nightclub.

In what has become an unwelcome but regular duty of his presidency, Obama was preparing to address an interfaith memorial service in Dallas for the officers. They were killed last Thursday while standing guard as hundreds of people peacefully protested the police killings of black men in Louisiana and Minnesota earlier in the week.

The attack ended with the gunman, Micah Johnson, 25, blown up by a bomb delivered by a police robot. The black Army veteran portrayed the attack on the officers as payback for the fatal police shootings of black men in Baton Rouge, Louisiana, and suburban Minneapolis.

Portions of both shootings were videotaped and broadcast nationwide, leading to fresh outrage, protests and scores of arrests. The killings also put the country on edge, heightened racial tensions and pushed the issue of the use of deadly force against black males by white police officers to the forefront.

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Obama will seek to bridge those issues with his tribute to the fallen five, which include a former Army Ranger, a Navy veteran and a newlywed starting a second family.

Some police officials blame the president for the rise in racial tension, saying he is insufficiently supportive of law enforcement. In comments since the Dallas shooting, Obama has urged the public to recognize and respect that police officers have a tough job.

Meanwhile, Obama has criticized by others for going to Dallas before visiting Louisiana or Minnesota, a sign that he is aligning with police over protesters.

As Obama landed in Dallas, Earnest said the president had called the families of Alton Sterling, the man shot by police in Baton Rouge, and Philando Castile, the Minnesota motorist shot by an officer, to offer his and first lady’s condolences.

The president, joined by his wife, Michelle, and Vice President Joe Biden and his wife, Jill, will also meet privately with the families of the slain officers as well as the injured to convey the support and gratitude for their service and sacrifice that has been expressed around the country. At least nine other officers and two civilians were injured in the attack.

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