He did...he shot him in the stomach. Brannon was a Vietnam ranger and combat veteran and had a high powered rifle. Dink didn't stand a chance against someone like that.
No, what he did was allowing a dangerous man to reach inside his car after blatently showing hostile behaviour. Brannon should have been seperated from his vehicle, and more so should not have been permitted by Dinkheller to come so close to him as to pose a physical threat.
He only was able to shoot Brannon in the stomache after he had been on the receiving end of the exchange moments prior to being shot dead.
Dinkheller had a chance until he allowed Brannon to come too close to him, and allowing him to retreat to his vehicle and reach in the cab for his M1.
It's a shame things had to go this way. From the video and conversation you can tell Dinkheller had no intention to use force, let alone deadly force, until his hand was forced. One of the 'better ones' lost that day.