The theory of State Capitalism had been sharply criticized by Trotsky, particularly in his books
Revolution Betrayed and
In Defence of Marxism. Trotsky's last struggle before his death was in fact against a petit-bourgeois opposition in the American SWP [the then US section of the Fourth International] which rejected the defence of the USSR against imperialism,
as well as the whole method of Marxism, dialectical materialism, both of which were inseparable. For a full criticism of this false theory, see Ted Grant's
Russia from revolution to counter-revolution, Part Four: The Nature of Stalinism (available online)....
Cliff stated (in his pamphlet ‘Trotskyism after Trotsky') that it was "necessary to defend the spirit of Trotskyism while rejecting some of his words."
The problem was that Cliff was not merely rejecting a few out-of-date words, but Trotsky's whole dialectical method, the very basis of Marxism.
Engels could have been writing about the SWP when he said, "
What these gentlemen lack is dialectics... As far as they are concerned Hegel never existed..." Trotsky's contribution to the understanding of Stalinism, which he developed over nearly 20 years, was one of his outstanding contributions to the theory of Marxism, and not some incidental extras. It is grounded in the method of Marxism. But, to paraphrase Engels, "As far as they are concerned Trotsky never existed..."