In the 19th Century, you had Pope declaring Americanism a sin, and denouncing the Enlightenment ideals of the men who founded this country (none of whom were, in turn, fans of Romanism).
Americanism is a heresy, which is a systematic error of opinion, not merely a sin, which is an individual error of thought or act freely chosen in the knowledge of the error. The heresy consists in separation of Church and state, and internally in the Church, of notions that the Church should be run democratically. It remains a heresy because that is what it is. The proper teaching is that the Church has a role and even a duty to inform the state on matters of faith and justice, (consistent, at it happens, with the 1st Amendment), and that the Church is a hierarcical institution locally run by the bishops and priests loyal to them.
In America itself, "Americanism" is usually used as a synonym of American patriotism, and that salutary disposition has nothing to do with the technical term among Catholics.