The American Constitutional system protects the rights of individuals. These protections could be called the traditional American political ideology.
Generally, a political ideology is characterized by having goals (a sense of how society should be) and methods (the best ways to achieve those goals).
The basic goal of traditional American political ideology is a well-functioning society arising from the free enterprise of the individuals comprising it.
The problem with this system is it is hard to understand and requires some governmental intervention to prevent abuse.
Since the American system is hard to understand, it has many competitors that are easier to understand. Communism was one of those.
The author of the following excerpt uses the word ideology to indicate political thinking that is too idealistic, without real-world understanding.
Like the Soviet Union of yore, contemporary America is in the grip of an ideology, a system of ideas not derived from any empirical study of the world around us, but which provides an account of the world, establishes an aim to be pursued and rules for pursuing it, and (most importantly) legitimates the power of some men over others. Another essential element of any ideology, as of any religion, is its demonology—an account of the enemy whom adherents must forever struggle against. Unlike personal enmities which arise through concrete social interaction, ideological enmities are established a priori by the ideology itself. In the ruling ideology of the Soviet Union, e.g., enemies included the bourgeoisie, revisionists, kulaks, and one especially nondescript class referred to simply as “enemies of the people.” In the ideology which prevails in present day America, the ideological enemies are the abstract groups denounced in Trump’s second Charlottesville remarks: racists, supremacists, haters and bigots, Nazis and the KKK. Ritual denunciation of designated enemies is an essential aspect of ideological rule, and leaders of an ideological regime cannot be considered legitimate without periodically making them. In the Soviet Union, communist politicians learned to spit out denunciations of communism’s demons in their sleep. (Trump’s Tergiversations on Charlottesville and Their Significance)
The linked essay is well-worth reading in full because it clearly describes the problems idealistic ideologies can cause and, by implication, why the traditional American system seems so open to attack.