Delusions are a social and psychiatric phenomenon, as is politics, and more importantly, political bias. Political bias is a rampant force in American society. Here I will demonstrate that political bias promotes delusional beliefs, and as a result American society is faced with a delusional-reality pathological-disease phenomenon of endemic proportions.
The loose definition of delusion is a fixed false belief. In psychiatry, the definition implies that the belief is pathological. Psychopathology is considered to be, in refernce to the affected, the manifestation of behaviours and experiences which may be indicative of mental illness or psychological impairment. Although common in several psychiatric conditions, they also occur in a diverse range of other disorders (including brain injury, intoxication and somatic illness). Delusions are significant precisely because they make sense for the believer and are held to be evidentially true, often making them resistant to change. 
HealthAtoZ.com  begins to describe delusions as this:
A delusion is an unshakable belief in something untrue. These irrational beliefs defy normal reasoning, and remain firm even when overwhelming proof is presented to dispute them.
And Minddisorders.com  describes delusions as follows:
A delusion is a belief that is clearly false and that indicates an abnormality in the affected person’s content of thought. The key feature of a delusion is the degree to which the person is convinced that the belief is true. A person with a delusion will hold firmly to the belief regardless of evidence to the contrary. Delusions can be difficult to distinguish from overvalued ideas, which are unreasonable ideas that a person holds, but the affected person has at least some level of doubt as to its truthfulness. A person with a delusion is absolutely convinced that the delusion is real.
These are key indicator signs of politically biased people, who more or less, hold onto delusional beliefs about their favored parties and members (and beliefs in the left/right binary system). The details and extent of the hold on the minds of those affected is beyond the scope of this article, but it is staggering. In terms of symptoms, theyre all there. Test this theory yourself on virtually anybody you know that proclaims to be either leftwing or rightwing, by presenting them with clear facts that shame their political party or favored member, and watch them jump through hoops dismissing and outright denying clear facts. Prove this theory by analyzing both historical and present day approval ratings during proven scandals and other landmark effects.
Political bias is nothing new. In 1974, during the final stretch of the Nixon-Watergate Scandal, Nixon maintained a 25 percent approval rating  in Gallup Polls. In 1968, Nixon had actually won in one of the closest elections in modern times, by a left/right margin of 511,914 votes, and totaling 31,783,783 votes in favor of him. As a minimalist scale of population margin we’ll just apply the approval rating to 50 percent of the people who voted for Nixon, or 15,891,891 politically biased people. Here’s another (low-ball estimate) way to attempt to measure PB: In 1972, Nixon had actually won by a landslide earning 60.7 percent of the vote, or 47,169,911 votes out of 77,744,027 total votes. 25 percent of 77,744, 027 would indicate roughly 19,436,007 politically biased people (in 1974), without even applying the 25 percent demographic to the national population.
Comparing partisan events and scandals (both individual and ongoing) to more modern times (which is beyond the scope of this article) is even more staggering (even in a minimalist context such as above). This is endemic (an ongoing and expected epidemic) by nature and definition, and even in those minimalist terms.
Further elaborations, and consequent arguments, to the definition of delusions can go as follows:
Delusions are often accompanied by hallucinations and/or feelings of paranoia, which act to strengthen confidence in the delusion. Delusions are distinct from culturally or religiously based beliefs that may be seen as untrue by outsiders. 
Even these extremist definitions of delusional can be justified, as follows: Dr. Drew Westins fMRI brain scan study  of politically biased people demonstrated that the affected twirl the cognitive kaleidoscope  to get the emotional results their realities desire, and then some of the brains reward centers fire to reward the process. During this process of justification, the other side is most likely blamed in some way to justify the reality threatening information. This theory is justifiable by the Hostile Media Effect alone, wherein studies have shown that politically-charged people take a paranoid approach to their personal interpretation of news, and take offense to it whether biased or not.
Since partisans may witness a favored leaders words/actions in some abnormal view or context despite its true meaning, and then form memories based on those interpretations, it can be said that those persons are hallucinating. Westins study demonstrated that partisaned brains reward centers reward them for lying to themselves about events and information, which would seem to strengthen confidence in the delusion. From there it can be argued that surely there are adolescence who decide to go different political paths from their hereditary indoctrinators, if not for reasons of rebellion alone. In that environment, the cognitive outsiders would see the opposing partisan view in an entirely different meaning, and thus hold the belief as untrue.
The DSM diagnostic criteria  for a belief to be considered delusional consists of the following:
(a)A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everybody else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. (b)The belief is not one ordinarily accepted by other members of the persons culture or subculture (e.g. it is not an article of religious faith).
So, according to the first sentence (a) of the DSM diagnostic criteria, a substantial amount of politically biased people are clearly delusional. Now the second sentence (b) could be used to attempt to argue that the politically biased arent in fact delusional, but that would be grasping at straws at this point. Although many of our current leaders (successfully) attempt to converge religious bias with political bias for more effective psy-ops crowd control, religious and political delusions are entirely different ballparks, or more precisely sports. However, blind faith indeed becomes the politically biased persons stance in regards to their earthly rulers. Finding faith in typically un-falsifiable ancient Biblical / spiritual figures / myths is a far cry from a person deliberately lying to themselves to justify what they just observed their living (non-spiritual) leader hero himself say. The equivalent would be if Jesus Christ Himself was a living public celebrity who consistently makes TV appearances, and is not only well known for publicly lying on a regular basis on a broad range of issues, but is categorically a liar just by association with whatever branch of celebrity hed be classified as.
If masses of people werent delusional in regards to political parties and figures, then they wouldnt even be able to use (b) as an argument to begin with, which brings us back to the case of political bias being the equivalent of a pathological disease of endemic proportions…
 Explaining delusions: a cognitive Perspective Vaughan Bell, Peter W. Halligan and Hadyn D. Ellis
 HealthAtoZ.com Encyclopedia, Delusions
 Encyclopedia of Mind Disorders, Delusions
 Poll: Approval Ratings Compared, CBS News (Nov. 2, 2005)
 An fMRI study of motivated reasoning: Partisan political reasoning in the U.S. Presidential Election, Drew Westin
 Political bias affects brain activity, study finds; MSNBC, Jan 24, 2006
 Diagnostic and Statistical Manual of Mental Disorders