Explanation
The losses of Germany on the eastern front are widely believed to be the most significant factor in defeating Nazi Germany and the USSR won the battle of Berlin, the final battle before the German capitulation. Thus Europe widely believed (for a good reason) that the USSR was the main contributor in defeating Germany. With the cold war the perception of the USSR became a lot worse in western countries like France and with increasing anti-USSR sentiment the view flipped to viewing the USA as the deciding factor. The USSR (and the Russian Federation today, even if its government is very anti USSR) viewed itself as the most important force in defeating Germany, especially because the USSR had the biggest amount of deaths. It is worth noting that the USSR was at least commercially allied with Nazi Germany until June 22, 1941 and there was an agreement between the nations on which parts of Europe each could invade and which where reserved for the other.
The decline of the french communist party is very well documented and was primarily a political matter. They committed many mistakes but also were dealt a serious blow by Mitterand in the 80s; finally, their voter base started voting far-right in the 90s. Not everything is a CIA operation.
The french communist party was also the most Moscow-aligned of all the western communist parties. This is a fact and was a serious factor in its decline since it suffered from its close association to the many failures of the Soviet Union (such as its foreign policy flip-flops and numerous human right violations), and ran all its important decisions by Moscow which prevented it from reacting quickly to the local political events. It can't be said to have been "infiltrated" however, it was all quite open.
I should also add that the french government wasn't too keen on NATO far-right paramilitaries, in that (1) de Gaulle was famously suspicious of NATO and (2) the very same paramilitaries (OAS) tried to assassinate him for advocating decolonization.
By that logic, all modern pro-NATO parties in the EU should have disappeared in the 1950s. You say the USSR has policy flip flops, but have you looked at the USA's foreign policy? As for human rights violations, I don't really know what you're talking about regarding the French Communist Party "natural political decline". Since Stalin's death in the 1950s the gulags were closed, famines had disappeared, and the USSR was an overwhelmingly peaceful nation that internationally provided help to emancipatory anti-colonial projects such as those of Cuba or Vietnam, while the US bombed the fuck out of them. Also, did you just say "nah" to the source I brought and simply disregarded it?
Both Hungary and Prague were huge PR disasters in Europe for the USSR though.
Yes, because of Yank propaganda. I don't see how they're anything remotely as bad as Vietnam or Korea, look at the figures of deaths. It's just that Europeans are racist as fuck and don't care about deaths of Asians, and American propaganda was much more pervasive.
I don't disagree. But that's the main thing that wasn't gladio, etc that helped fuck the parties in Western Europe.
If 10% the standards applied to western communist parties had been applied to the rest of parties, communists would have ruled Europe. My point is it's mainly gladio + propaganda that did this