I would highly recommend watching this video as I am about to butcher the explanation.
Essentially communism and critical theory literature both hold that the effects of prosperity under capitalism are chains on the population that keep them from engaging in "glorious revolution". They believe that if the people were to rise up together and abandon capitalism a utopia would arise. To encourage people to engage in revolution they believe it is necessary to, within the confines of democracy and capatalism, corrupt artifacts of prosperity so that the people see them as chains and cast them aside. You can probably see where that is going. Corruption of culture, corruption of monetary systems, social welfare programs that disinsentivize prosperity, etc.
They also hold that democracy is an imperfect system because differences in opinion that require democracy would be sanded smooth if true equity was acheived. That differences of opinion are purely a result of variable class (or in critical theories case, race, gender, sexuality, etc.)
You can learn more about the communist/critical view of, and plans to end democracy here.
Anyway, per the original video, the communist/critical literature holds that if you cannot convince people to undertake revolution because the "chains of prosperity" keep them complacent, or you know, prosperous, it would be optimal to circumvent democracy to install an illegitimate government who, unchained by the will of the people, could begin to dismantle the chains of prosperity. We've been seeing that for decades to a certain degree, but if that is their end goal, Biden is their antichrist.
I would say that it began in ernest when the warning of Marine General Smedley Butler exposed the plot of a Communist coup by the elite class. McCarthy was 100% correct, but was silenced by cancel culture.
Yes this has been underway for many decades. We just have the "pleasure" of getting to fight the final battle. It will be ugly.