I see the role of these fringe ideologies as emerging from the confluence of two social factors.
1. The myth of the "Real American". It is arguably the basis of the Tea Party movement and the distinction between "working" and "not working" people which fueled Trumps populism (
Source,
Source). In fact, this myth has been invoked multiple times throughout the history of both America and Europe. The short-lived period of success of Fascist Vichy France, along with its reactionary politics, was based on a myth which has chilling parallels to what many Right-Wing Americans espouse today. The form of the myth is that the "real people of the nation" are the ones living outside of the cities, doing the real work and leading hard and pious lives. In contrast, those in the cities are the Jews, Socialists, Communists, Blacks, Foreigners, and their collaborators, who do not really serve any function are are living off of the surplus (Marxist term used ironically) that is produced by the real people. This ideology led to policies which went beyond what the Nazis demanded.
Source.
2. The diminishing importance of social roles in our concept of ethics. The Ethics which underlies the "Real American" is essentially Aristotelian.
Nichomachean Ethics argues that the best life a man can live (Au Zen, "living well") consists in him effectively performing all of his social roles. These roles were determined by the various social relations a person had, as a friend, a juror, a soldier, a member of a household, etc. I am not here suggesting that Aristotle would be a Republican if he were alive today. Instead, I simply wish to emphasize the parallel between this role based "Virtue" Ethics and the thinking of conservatives. This way of thinking has its greatest champion in the Church, with the Catholic Church being the most prominent in its intellectual contributions to this body of thought. However, it is not the Ethics of the Enlightenment and as such has been challenged and is in decline as the relevant Ethics of public policy today. Nevertheless, conservative society is still marked by these essentially Aristotelian attitudes, which proscribe roles for everyone based on identities which must be externally obvious and at the same time relatively unchanging in order for everyone to know everyone's role and therefore collectively enforce the dominant ethic. Evidence that conservatives do think this way is almost unnecessary -- such attitudes are written into the definition of conservatism (unfortunately I'm unable to provide actual evidence at this time).
As the power of the Church has declined over the years, so has the influence of this way of thinking. It contrasts especially with the ethics of the market, "Marketism" (Or Marxism?), in which value is not guaranteed and instead is only what others are willing to pay. Americans who engage in market competition, either as poor workers or as business owners therefore encounter this ideology. The proponents of this sort of Ethic often champion freedom in one form or another -- we can count among them Ayn Rand, Robert Nozick, and Karl Marx to name a few.
Virtue ethics also contrast with Enlightenment theories like Utilitarianism and theories of rights. These are what are taught in school and the basis of modern jurisprudence as well as the tools which are used in public discourse on current events and public policy. I'm intentionally omitting Kantian ethics from this list since nobody knows what he is really arguing and attempts like that of Rawls essentially lead to similar policies as utilitarianism. There are so many authors writing in these traditions that I can hardly list them, and because I haven't researched it, I don't actually know which are the most relevant.
Thus, there are four Ethical theories in competition today: Virtue Ethics, Utilitarianism, Rights systems, and Marketism.
Now, it is possible to argue effectively and cogently for a
complete right-wing agenda from the point of view of only Virtue Ethics. Because this Ethic does not presuppose a universal foundation, it is easily interpreted to support whatever traditional values already exists in the society, and it is difficult (or maybe impossible) to critique those values from within virtue ethics. If we divide the right-wing agenda into two parts, one being social conservatism and the other being laissez-faire economics, we find that Rights systems and Marketism conflict with the first and utilitarianism conflicts with the latter.
Right-Wing politics requires a coalition, so they will naturally bring in people believing in ideologies founded on one or more of these bases. But the pundits and spin doctors that wish to create messages that appeal to the entire base therefore have a problem: How to message in a way which appeals to people who ascribe to such starkly conflicting ideologies. The answer, of course, is to simply avoid any logical discussion at all. Instead, craft arguments based on all of the natural flaws in human psychology. Because 50% of the population has an IQ below 100, it turns out that this strategy works surprisingly well!
Messaging can't be based on virtue ethics simply because nobody learns virtue ethics anymore. But its influences still exist in conservative thinking in a half-formed and sophomoric way. Thus, Right-wingers are susceptible to messages that lead them toward thinking along the lines of how they are fulfilling their roles for society while others are not doing so or actively working to undermine America. This is already very conspiratorial, but it is not itself based on a flawed framework except insofar as Aristotle is flawed. But it doesn't draw out any real contradictions in Aristotle because it is an extremely abstract and weak understanding of the relevant ethics. Instead, it is just a form of nationalism which has the potential to erupt into populism and even Fascism. The sparks that bring about these eruptions are the conspiracy theories which right-wingers are unable to properly think through precisely because they are unaware of the nature of their own ethics.
Much of my thinking in this post was inspired by the book
After Virtue by MacIntyre and the Psychological research of Jonathan Haidt.