No it is not. The definitive answer as to what is, or is not, a psychological disorder is the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) (5th edition release has been delayed to 2013). A search of the document for the word "liberal" (with wildcards) only turns up three entries.
Application of Trait Theory in Personality Synopsis at ALLPSYCH Online
Openness to experience refers to the dimension ranging from outgoing, liberal, interested in new things, and imaginative to reserved, conservative, traditional, and conforming.
allpsych.com/personalitysynopsis/trait_application.html
Post Traumatic Stress Disorder Related to Prisoners of War in AllPsych Journal
Once liberated, soldiers are given a medical exam and ... years after the former prisoners of war have been liberated and readjusted to life. Sometimes this happens when other
allpsych.com/journal/pow.html
Trait Theory in Personality Synopsis at ALLPSYCH Online
Openness to Change liberal versus traditional Perfectionism compulsive and controlled versus indifferent Privateness pretentious versus unpretentious Reasoning abstract versus
allpsych.com/personalitysynopsis/cattell.html
Two of the links are about the trait of liberalism without making any statement in regards to any psychological disorders. The second return only got caught in the search because it mentions "liberation" in the context of being freed from captivity, and how that applies to PTSD. None of them even hint at there being any association with a psychological disorder.
Your citation of the two sources are a bit problematic. First of all, Michael Savage is a well known ideologue. You even use WorldNetDaily as your citation for him. I would suggest that going to professional psychology sites where there are peer reviewed papers is a better and more impartial source. Not books, which are not subject to that peer reviewed process.
In looking over a synopsis of Dr Rossiter's book, in a nutshell, the book's thesis is, "My political views are so obviously correct that anyone who doesn't accept them just has to be nuts." It presupposes the truth of a right-wing political outlook and then tries to plumb the reasons why other people do not accept this truth, the conclusion being that they have to be in massive denial.
This is not particularly neutral either.
Upon further research, it appears that Dr. Rossiter's book is a direct rebuttal to a government funded study titled Political Conservatism as Motivated Social Cognition. A study published in 2003. Most of the claims in Dr. Rossiter's book are not so subtle reversals of the conclusions reached by Drs Jost JT, Glaser J, Kruglanski AW, and Sulloway FJ (listed authors of the paper, which HAD received peer review in the Psychological Bulletin as well as being supervised by the National Foundation as well as the National Institutes of Health). As a counter point to some of the assertions by Dr. Rossiter, Dr Kruglanski states (about this study in particular):
"The variables we talk about are general human dimensions," he said. "These are the same dimensions that contribute to loyalty and commitment to the group. Liberals might be less intolerant of ambiguity, but they may be less decisive, less committed, less loyal."
Dr. Kruglanski added a disclaimer that their study "does not mean that conservatism is pathological or that conservative beliefs are necessarily false".
Some of the items that Dr Rossiter objected to in particular were statements like:
"This intolerance of ambiguity can lead people to cling to the familiar, to arrive at premature conclusions, and to impose simplistic cliches and stereotypes."
and
The core ideology of conservatism stresses resistance to change and justification of inequality and is motivated by needs that vary situationally and dispositionally to manage uncertainty and threat.
Neither of those statements make any particular value judgments, unlike Dr Rossiter's book.
As a counter to the Political Conservatism as Motivated Social Cognition study, there is Bright Minds and Dark Attitudes: Lower Cognitive Ability Predicts Greater Prejudice Through Right-Wing Ideology and Low Intergroup Contact, published by Sage Journals. This was published well after Dr. Rossiter's book, and carries a message that aligns with the political outlook that Dr Rossiter espouses, yet this paper makes no judgment on liberal (or "left") ideologies being a mental illness. Instead the paper focuses on:
Despite their important implications for interpersonal behaviors and relations, cognitive abilities have been largely ignored as explanations of prejudice. We proposed and tested mediation models in which lower cognitive ability predicts greater prejudice, an effect mediated through the endorsement of right-wing ideologies (social conservatism, right-wing authoritarianism) and low levels of contact with out-groups.
Furthermore, there are many nuances that seem to get ignored in social discourse regarding conservatism and liberalism. One can't really equate conservative with right-wing in all cases. For many, right wing is a fiscal policy stance, while conservatism is a social policy, and people cross over those definitions in numerous permutations.
So again, Mr Savage and Dr Rossiter appear to have political and ideological motivation, and are using the hallmarks of that rhetoric. There is no evidence their statements regarding liberalism (or any other political viewpoints) are supported as being a psychological disorder.