It was already a tragic week in the United States, with the deaths of Alton Sterling in Baton Rouge and Philando Castile in Minnesota in police shootings.

Downtown Dallas was in lockdown early Friday after snipers shot 11 officers, five fatally, during a protest over deadly police shootings of black men elsew.

Three people were in custody and a fourth suspect exchanged gunfire with authorities in a parking garage at El Centro Community College into the morning, Dallas Police Chief David Brown said.

NBC Dallas Fort-Worth reported the fourth suspect had been “Neutralized” at around 2:45 a.m. Earlier, he had told police negotiators that “The end is coming” and that “T are bombs all over the place in this garage and downtown,” Brown said.

The president went on to tell reporters, “T is no possible justification for these kinds of attacks or any violence against law enforcement. Anyone involved in the senseless murders will be held fully accountable. Justice will be done.” Referring to law enforcement officials, Obama added, “Today is a wrenching reminder of the sacrifices they make for us. When people say ‘black lives matter,’ it doesn’t mean that blue lives don’t matter.”

T will plenty of discussion going forward as we learn more about last night’s murders and what can be done to prevent future violence, but t are some early indications that some intend to take the debate in an ugly direction.

Joe Walsh, a former Republican congressman from Illinois, wrote via social media last night in response to the Dallas slayings, “This is now war. Watch out Obama. Watch out black lives matter punks. Real America is coming after you.”

Perhaps realizing that these are the kind of remarks that invite a visit by the Secret Service, the former GOP lawmaker deleted the message soon after, but added a related comment, insisting the president’s rhetoric is responsible for the murders of police officers.