I’m not at all sure Stalin could have done it without Lenin, and of course there was getting Trotsky out of the way. But it’s certainly important to know that they were functioning in a political culture with few features that USAmericans would recognize as democratic. The Tsar had been called “Autocrat” as a term of respect and “Little Father” as a term of affection. In such a culture, the line between authoritarianism and totalitarianism is very blurry.
You also need to factor in the relative isolation of the Russias up until WWI, especially for the workers and farmers who may have been sent west to fight; the global economic mess leading into the 30s; the further problems left over from the Russian civil war; and how much sooner WWII started in Europe than it did for the US.
Stalin had a lot on his plate in the period you cite, and a culture that said it was his job to manage just about any way he could, at least if he wanted to retain power. He was not the brilliant theorist and communicator that Lenin was, and may well have harbored resentment of Russian hegemony in the region, being Georgian. It’s a very complex situation that has to be understood in its own context.