The left isn't behind the military? According to whom?
Their lack of support and willingness to serve. Are you denying the vast majority of military personnel, especially careerists, lean right? Are you denying it's the Left Wing that regularly attacks the military, cuts their budget and demeans those who serve as "war mongers", "too stupid to get a real job", etc?
Feel free to poll the veterans here. While some lean Left, most lean Right. The Left Wing knows this and it's one of the reasons it dislikes the military.