As the week comes to a close, America has seen tragedy unfold on two fronts; the country watched in horror as two black men in separate states were killed by police; one who was selling CD's, the other during a traffic stop, parts of each bloody incident recorded, their images indelibly seared on the public's minds.The other was the killing of five law enforcement officers in Dallas, with several others injured by a sniper. And the two major candidates for president have weighed in.The comments by Republican Donald Trump and Democrat Hillary Clinton are a reminder of the different approaches each has taken during the campaign in responding to issues around policing and the deaths of African-Americans in police-involved killings.Presumptive Republican nominee Donald Trump released a statement Friday morning, referring to the killing of the officers as "an attack on our country" and calling for love and compassion -- a noticeably more measured stance than he has taken in the past."We must restore law and order. We must restore the confidence of our people to be safe and secure in their homes and on the street," continued the statement posted on the candidate's Facebook page, to which he tweeted a link.Trump also made his first mention of the police-involved killings earlier in the week of two African-American men -- Alton Sterling in Louisiana and Philando Castile in Minnesota."The senseless, tragic deaths of two motorists in Louisiana and Minnesota reminds us how much more needs to be done," he said. Only one of the victims, however, was a motorist. Sterling was killed after a confrontation with police outside of a convenience store. Police can be heard on video saying "gun" before firing at Sterling, who is restrained, at point blank range. Police refused to say if a weapon was recovered.In Castile's case, his girlfriend said that he told officers that he had a licensed pistol. An officer can be heard on that video shouting that he told Castile "I told him not to reach for it" while Castile's girlfriend, Diamond Reynolds, can be heard telling the officer that he told Castile to retrieve his license.Trump later released a video message to ABC News that paid tribute to the lives of the slain officers as well as Sterling and Castile.Trump's Democratic rival also tweeted about the killing of the Dallas officers.Clinton had commented on Sterling's case earlier, when on Wednesday she applauded the Department of Justice 's decision to investigate the killing."From Staten Island to Baltimore, Ferguson to Baton Rouge, too many African American families mourn the loss of a loved one from a police-involved incident. Something is profoundly wrong when so many Americans have reason to believe that our country doesn't consider them as precious as others because of the color of their skin," Clinton said in a statement. On Thursday, she tweeted about Castile's death.Although each candidate this week showed concern both for law enforcement and for those troubled about police-involved killings of African Americans, that has not always been the case.Trump's statement Friday contained his first public expression of empathy for any African-American victim of police violence during his campaign, though even in this statement he did not mention the race of either Sterling or Castile. Many people in the country are outraged and aggrieved over what they say is a pattern of systemic violence involving police and black victims.Clinton has expressed sympathy with the concerns of the Black Lives Matter movement, which advocates for fair and equal treatment of African-Americans by police and the entire criminal justice system. Trump, on the other hand, has derided Black Lives Matter protesters.In a September interview on Fox News, Trump said of the movement "I think they're trouble, I think they're looking for trouble." He added, "I think it's a disgrace ... Give me a break, all lives matter."Trump also drew criticism during the campaign for tweeting a graphic containing false statistics about black-on-black crime while Clinton has tweeted and spoken of concern about the issue of police brutality.When Trump was asked during the ABC News Republican Debate in February how he would heal the nation's racial divide, he chose not to focus on victims of police violence, but instead solely defended police."There is a divide," Trump said. "But I have to say that the police are absolutely mistreated and misunderstood and if there is an incident, whether it's an incident done purposely, which is a horror, and you should really take very strong action, or if it is a mistake, it's on your newscasts all night, all week, all month, and it never ends. The police in this country have done an unbelievable job of keeping law and order."