Civilians in the military?

I'm still trying to figure out what Senator Joe Biden meant here. In reference to the story in my last post about the Guard going to the border, he said:

"We have stretched these men and women so thin, so thin, because of the bad mistakes done by the civilians in the military here, that I wonder how they're going to be able to do it," Biden said, also on ABC.

What? I'm confused. Who are these civilians? It could possibly be targeting Bush, but who else? The generals making the bulk of the decisions in the military aren't civilians. He could be talking about people like Donald Rumsfeld and others in the Department of Defense. They may be civilians, but are they in the military?

I have no military experience, which makes me a bit confused as to what he means.

Of course, Biden has no military experience either. He's been a U.S. Senator for 34 years - more than half his life. You have to be 30 to be a U.S. Senator. He was elected at the age of 29, but turned 30 just one month and 14 days before being sworn in. Previous to his career in the Senate he was a lawyer for 4 years.

I'm guessing he's not a military expert either.