Under other circumstances, I could imagine the NRA describing the Dallas incident as: "An armed citizen exercises his Second Amendment right and strikes back at agents of a tyrannical government that oppresses his fellow citizens."
...except he's black and was responding to violence against blacks. Certainly a despicable act, and I pray we don't see more murder, riots, terrorism, etc. But the NRA's silence until recently is remarkably hypocritical.
Incidentally, I am concerned about the following scenario: One or both law enforcement officers (LA, MN) are acquitted (as similar previous cases suggest they will be). Frustrated, angry, scared supporters riot. Images in the media of civil unrest and opportunists using this as cover for crime/looting, perhaps with more violence against law enforcement by minorities, play into racist elements of Trump's campaign support.
http://www.newyorker.com/news/news-desk/the-silence-and-violence-of-the-n-r-a