In the main, the democrats have no problem cutting Defense spending. The DOD is not a dem constituency. So, they accomplish two things at once by allowing the sequester to occur. First, they hurt a Republican constituency. Second, they can foster division and rancor on the right by making the Republicans seem callous or incompetent or both.
Apparently it isn't a Republican constituency anymore either.
House GOP unafraid of defense cuts
House GOP thinks unthinkable on defense cuts
I don't think Ronald Reagan would recognize the current crop we have in there.