It all depends on where you are talking about, I suppose. In most winter range areas near me the snow blows off the low ridges exposing feed and piles up in between. The elk by the hundreds eat the exposed feed to the 1 inch tall. Many of the mule deer stay up in the timber for the most part and go from tree to tree eating the available food for as long as they can. They will drop lower if it gets really cold, clear below the elk into peoples' yards or to the river bottom. They never get fat. Harsh winters really hurt them.
There are far less cattle grazing the forest and the private in this area than when I was a kid.
I don't blame our mule deer problems on any one thing and believe that all of the detrimental factors listed in the posts above are legit. The problems vary from one area to another, and I think it is best to concentrate on making the changes that are doable rather than wishful thinking or focusing on our personal pet peeves. The area where I spend a lot of time would benefit from predator reduction, but realistically it will be very limited if it ever happens at all. Elk numbers could be lower and would help some, but they have been trying to reduce elk numbers around here for years with little success. I don't see that changing.
I believe that we should regulate ourselves first. We simply can't keep increasing hunter pressure on a declining population and expect any other change to make much of a difference.