Sanders receives most campaign contributions from active duty military. More so than any other candidate and president Trump.

[citizentruth.org]

Why does Sanders have such high support from the military, even more so than veteran Pete Buttigieg? It's pretty simple, he has a very long career of consistently supporting peace and nonintervention as well as his advocacy for veterans which has significantly improved the VA.

Of course the upper echelons of the military don't share the support of the rank and file. Sanders' policies are detrimental to recruitment. The GI Bill is a very significant recruitment tool because it offers poor young people a way to get into college and improve their lives. Sanders' policy of student debt cancellation and making college affordable would undo this incentive. In fact, his entire agenda of helping the working class is opposed by the bigwigs because the military relies on keeping poor people poor with few options to bolster the ranks. If working class people actually have opportunities to live decent prosperous lives, recruitment plummets.