When the attempt wasn't made at all. It is always better to try something and fail than never to try at all. At least from failure you learn.

Khmer Rouge followed by Shining Path

is it stupid to say japan because my jaw dropped when i learned about how radical the JCP used to be but now its a socdem type organisation. i haven’t even got into the cold war history of the party and i’m scared to find out the details of what the CIA really did to them 😭

Ceauşescu, probably

Banned abortion
Was a dick to Roma people
IMF loans / austerity

well, even if posadas didn't do shit in argentina that's gotta be it, right? ufos, aliens as revolutionary allies, nuclear apocalypse. posadism is one hell of a drug. and what's even funnier is that there are still some posadistas in argentina, not so long ago i looked them up and they're like 3 dudes (i think one was his son or related to him?) who meet and talk i guess, they can't do much more lol.

Vergissing van Troelstra, also known as 'Rode week' (red week). This was when Dutch socialists, led by Pieter Jelles Troelstra, tried to launch a revolution in the Netherlands

Scandinavian social democracies and the SPD are examples of total failures of parties which once were revolutionary.

I'd go with the Khmer Rouge. However, there are lots of ways to define "worst":

• The Khmer Rouge was simply genocidal, and they were killing loads while in power.
• The Japanese Communist Party is very ineffective. Barely anybody in Japan even considers them. While their revisionism makes them akin to a SocDem party of any other nation, the staggering part is their size, that being as big as an after-school club.
• The CPUSA became full of revisionism after WWII.

Does worst mean fell into internal revisionism the most, was least able to grow and spread thruout the people, or least able to survive the USA? I mean, where does one draw the line between a communist party that is incredibly revisionist (ie, the CPUSA), or a bourgeois party that brands itself left-wing (ie the Movement for a People's Party)?

PatSocism/MAGA "Communism" probably

Maybe the Paris commune, but I am not very knowledgable on it.

On a sidenote, your questions do seem to be very specific, comrade. I don't know how to word it, but there is something about the types of questions and their wording that seems off to me.

Not the worst but the most unfortunate is spartakus league.

1971 Turkish military memorandum

Zohran Mamdani

PDPA trying to aggressively promote atheism, which helped set in motion the collapse of the Soviet Union.