I honestly don't get this bizarre notion that flag-level officers are presidential/VP material. It comes up every election, some general/admiral is floated as a potential Pres or VP pick because....reasons. Nobody could even tell you what their politics are most of the time, but they supposedly make Good Leaders, and that's apparently enough.
I think it relies on the assumption that anyone who rises to that level of command is a competent serious person, and their competency will bleed over into politics, which never seems to happen. There have been rarities, like Ike and Grant, but we mostly don't pick from the military when we elect Presidents.