The mainline American Communist Party (Communist Party USA) has been a LARP put on by the Federal Bureau of Investigation for decades (cf. The Man Who Was Thursday).
Traditionally (and if the mainline adjective didn't tip you off) CPUSA belongs to a school of communism known as anti-revisionism, which for the sake of brevity I will define as "Stalin was a p. cool guy, you know?"
People got kind of sick of the whole FBI LARP thing (which I don't get, who wouldn't want to LARP on the taxpayers' dime?) and engaged in the time-honored communist tradition of splitting from a party and starting another one. The PLP is one of the oldest (to use a tech term) forks from CPUSA still in operation. IIRC they originated in the 60s.
Since they don't have their origins in the Sino-Soviet or Sino-Albanian split they don't really have a ton of cache in anti-revisionist circles.
