One answer to your question lies in the psychological function of "projection" - that is, identifying with someone or something closely so that it is, in a sense, a symbol of yourself. Thus when someone criticizes the symbol, it translates into a criticism of yourself. We've all had this experience - either with a new car, a friend or relative, an opinion we hold about something, etc. In other words, some of those on the right are identified with the president and a criticism of the president translates into a personal criticism. The problem is that some on the right as SO identified with the president (because of 9/11, he is their savior), they have on some level idolized him and there is no room in their worship of him for criticism. To criticize the president is to attempt to bring him down from the pedestal upon which they have placed him, it attempts to de-deify the president and make him a flawed human. And if that happens, what does that say about them and, more importantly, where does it leave them... without a savior. An unbearable situation. A lot of this is unconscious but we are seeing the results of it in their rabidity.
Read this article by the Lbertarian Lew Rockwell. In it he examines the right/left balance of power and chronicles the shift over the past decade. Among other things, he specifically addresses the rabid hatred coming from the right, their worship of the president, and their radical change from being pro-small government to embracing government as the solution to all problems.
It's really an interesting article, bearing in mind that the author is a Libertarian and the article is pro-Libertarian which traditionally has been ideologically opposed to the left. Now, however, he finds a closer relationship between the ideology of Libertarianism and the ideology of the left whereas they used to be closer to the right.
The Reality of Red-State Fascism
http://www.lewrockwell.com/rockwell/red-state-fascism.html