Not Russian "fascism", but outright Leninism which applied an elitist model by a single leader that Marx never contemplated beyond a dictatorship of the proletariat. Not a party apparatus and bureaucracy with a single leader at the top.
Worse still later a single leader (Stalin) who would purge his own party of anyone who opposed him on virtually any issue. Particularly Leon Trotsky who steadfastly remained a proponent of global socialist revolution that Stalin wanted no part of.
Totalitarianism isn't confined to fascism. It can fundamentally exist on either poles of the political spectrum. As for authoritarianism, that can potentially happen along all points of the political spectrum. Particularly where corruption plays a major role in a society no matter what ideology may or may not be predominant.
An important aspect of the extreme right is their hallmark signature of using a democracy as a catalyst to gradually seize power, as opposed to the extreme left inciting a violent revolution with a favorable outcome.
Yet in American political culture they use terms like "radical" this or that, not to truly define opponents, but only to disparage them. When the common denominator of real extremism often comes down to whether they condone "a means justifying an end". Those very few who may be willing to operate outside the law and/or an existing constitution.
