We dont allow conspiracy theory here, but I will do my best to answer your question earnestly, all the same.
More or less:
The US political system does not tolerate 3rd party voices meaningfully. As such, the system stabilizes on 2 basic ideological camps.
Generally speaking, "Negative Emotional Experiences" have stronger memory potentiation than positive ones. This is not a suggestion, this actually holds up to scrutiny.
As such, it is "advantageous" to both ideological encampments to demonize the other, and assign blame of any and every negative emotional episodic memory with the actions of policies of the *other*, while attempting to distance themselves from the same action by the other camp.
This evolution gives rise to specialized propagandist thinktanks that specialize in shaping the emotional perceptions of the electorate within target demographics, such as Heritage Foundation, and company. These groups cluster around "Political Action Committees", and other funding vehicles, to push specific narratives and policies designed to foster this ideological isolation and emotional reinforcement in the electorate, in order to more reliably and assuredly produce real voting results at election times.
Many many Many decades of this later, you have the kind of post-modernism that Jean Baudrillard waxes philosophical about (literally.) Things have long since stopped being about actual things that happened, and are now entirely based on symbols of, representations of, and emotional perceptions of, past events or policies. Much like the "Hatfields and McCoys", at some point, nobody even remembers what the initial points of policy disparity *even were*, only that "The other party" is bad, and to blame, and must be stopped at all costs, with only bland and flimsy generalizations given, instead of specific, actionable policy contentions. As such, any actual ability to establish dialog between the parties breaks down, since nothing of any actionable substance exists to be communicated or worked on in the first place. There is only "Our Policy" (which is intrinsically good) and "Their policy" (Which is intrinsically bad).
These same groups (thinktanks and PACs) are specifically engaged in political engineering through public perception management, and make extensive use of targeted advertisement, social engineering with preferred entertainment sources or figures, and statistical application and study of things like Sunk Costs, and Blowback effect. They use these tools to select policies, agendas, and investment strategies that will be most favorable to the ideological encampment they service, with no other considerations taken. (Like what is *quantitatively or qualitatively best FOR THE NATION*)
Generally, people in the US (I happen to live here), are already suffering from "Information overload" and "Attention deficits". Meaning, the electorate is becoming less and less *capable* of observing, understanding, and voluntarily counteracting the political machinations of these interest groups.
Conditions are favorable to, and continue to become *MORE FAVORABLE TO*, the policies and practices of these kinds of political engineering groups, with a naturally more and more ideologically segregated and less and less rational national mindset about any specific sets of policies.
Due to this, a breakdown in actual quality of candidates emerges, as the candidates *THEMSELVES* are products of many decades of this political manipulation process, and *THEMSELVES* hold unrealistic, non-specific, generalized and non-actionable views about policy. Since the public is likewise losing the ability to discern this, or to discern actionable policy from nonactionable policy, through purposeful activity of these groups, there is no balance or check against it. It just continues to snowball.
Our current political deadlock in the legislature, with people there that very clearly should not be there, and people holding high offices that have no real qualifications to support them holding them aside from generalized emotional or general political-alignment ones, with a highly polarized electorate, *Naturally Follows.*
I do *NOT* enjoy having this revelation.