Communism is compatible with the separation of powers contrary to marxism-leninism and the right-wing/fascist culture.
To develop a bit about the common problems caused by these 2 cancers:
In a marxist-leninist system there's only 1 party whereas in a right-wing/fascist country the parties are financed by the rich which gives a systematic advantage to the corrupt politicians. The political leaders are more or less indirectly elected by the capitalist apparatchiks like the "great electors" in the USA. How can you call the USA a democracy since people give their vote to someone who can betray them anytime he wants when it comes about choosing the president by the way?
In both systems people don't choose their leader and neither the right-wing/fascist activists nor the marxist-leninist ones never offered anything to give all the parties the same financing.
In a marxist-leninist or a right-wing/fascist system there isn't any separation between the leading party and the economical power. When no law prevents a company boss from cumulating with a political power the capitalist apparatchik can easily prevent the vote of laws that would prevent it from murdering people with petroleum-based fuels or pesticides for example. When many politicians work as "advisors" for the companies then can easily receive corruption bribes disguised as professional commissions. To make it short those who control the economy can trample the workers' rights while getting always richer and strenghtening their power.
In both systems to prevent the economic leaders from trampling the workers' rights and neither the right-wing/fascist activists nor the marxist-leninist ones never offered anything to change it.
In a marxist-leninist or a right-wing/fascist system nothing is done to protect the freedom of the press (everytime a dictator makes a coup d'état he notably takes the control of the medias by the way). In both systems the medias aren't neutral because they are controlled by the state and/or the company bosses and they can't denunce the corrupted politicians and the slavers, public-poisoners bosses without suffering any retaliation.
In both systems the political/economic power can trample people's rights without being denunced and neither the right-wing/fascist activists nor the marxist-leninist ones never offered anything to change it.
Since the right-wing/fascist culture and marxism-leninism are both based on the concentration of powers whereas democracy is based on their separation is it surprising to see so many common problems in the USA like in the ex-USSR?
Mainly because we aren't really a democracy. We are a representative republic. But, that's too much of a mouthful to describe the US, so, "Democracy" it is.