If, in 1955, you were sitting in a room with other people who wanted to topple America, what would your plan be?
You most likely would look for pre-existing divisions in American society that you could exploit (e.g. race, socioeconomic status, urban vs non-urban, university educated vs not university educated, etc.).
You would look for ways to achieve massive demographic shifts. The best way to do this would be to promote immigration, both legal and illegal, with a heavy emphasis on bringing in people who are likely to be more sympathetic to/in line with Communism/Socialism.
You would subsidize youth pregnancy and out of wedlock children (when you weren’t pushing abortion), building government dependency.
You would push for secularism, and to diminish and denigrate the role of religion in society. This could be done in a variety of ways - including infiltration of the churches, eradicating all talk about religion in public schools, and pushing a secular narrative in the schools - including efforts to denigrate the character and integrity of those visibly active within the religious community. You would also push the narrative that science has all the answers, and that science and religion are mutually exclusive.
Etc. In other words, you would do what has been done in America for the past 70 years.
You would also push to destroy organizations that establish character in youth like the Boy Scouts. You would ostracize them for prejudice against gays in the scouts (scoutmasters). Then you would demonize them and bankrupt them with lawsuits for admitting pedophiles who preyed on children. The young boys were just pawns in their evil scheme.