The GOP is afraid of Hagel because he, very sensibly, realizes that the DOD needs to be cut. This is anathema to the GOP because the GOP is beholden to the "defense" industry. Hagel realizes that the world has changed since the Russian Bear was poised across the Fulda Gap and that we do not need to borrow any more money from the Chinese to defend our competitors against nations that no longer exist.
We are dead broke and the sooner we make the cuts we need, the better chance we have of staying alive as a nation. Our spending is the biggest threat to our national survival.