How did Bolsheviks win the argument so decisively ?

The Bolsheviks lost the only open election they campaigned in 1917. They originated as a hardline faction within a larger party, the Russian Social Democratic Labour Party.

There were thinkers like Bernstein or Kautsky who had more moderate proposals for gradual democratic socialism. Lenin’s entire thesis for a Russian revolution was that Russia was developed enough in terms of capitalism for a revolution. Capitalism was needed in some limited form.

I’m curious how he and Stalin managed to put it on such a violent trajectory and Lenin won every significant Congress. In the West they had many supporters until at least the Khrushchev speeches and the Cold War.