The theme of a great gunslinger or lawman who has lost his nerve, is not a very rare theme in a western movie. The Intruders was such a movie (1970's, made for TV).
As I recall:
Around about the same time that I saw The Intruders on TV years ago, another such movie was put on. As I recall the sheriff or marshall had come near dying from a gun fight; and after the near death from gun shot, he had lost his gun nerve. He was going around town not wearing a gun living on his reputation.
In the climax, a gunslinger came to town & began acting as a bully. He displayed dazzling speed on the draw and deadly accuracy with his fire. Eventually the gunslinger confronted the sheriff & forced a gun fight with him. But when the gunslinger reached for his gun, he didn't even get it all the way out of the holster before the sheriff shot him (probably in the heart). As the gun slinger died he had an amazed look on his face and commented on how he didn't even get his gun out before the sheriff/marshal outdrew him & shot him (last words of the gunslinger).
Does anyone recall that movie and its title?
I think I saw it in the 1970's on TV, but it may have been made before 1970.
Subject: TRYING TO GET THE TITLE OF AN OLD WESTERN -- SHERIFF LOST NERVE THEME 
