Any German officer standing two feet from Hitler prior to July 1944 could have blown his brains out.
Still doubtful about that. That Jewish German kid who tried to assassinate Hitler during the 1930s was close enough in range to shoot him (at least two feet if I remember my textbook correctly), and he failed, and he was highly motivated to kill him due to wanting to stop Hitler’s Jewish persecution (not to mention most likely had enough training in firearms to be able to use one). If he failed there, not sure how a soldier could pull that off against Hitler (not to mention Hitler by that time would have been as paranoid as Stalin was late in his life, so he’d probably have anyone close to him shot just on the mere off-chance that he was planning to backstab him).