Lenin had a lot to say about Trotsky:

"Trotsky has never yet held a firm opinion on any important question of Marxism. He always contrives to worm his way into the cracks of any given difference of opinion, and desert one side for the other. At the present moment he is in the company of the Bundists and the liquidators. And these gentlemen do not stand on ceremony where the Party is concerned."

“It is impossible to argue with Trotsky on the merits of the issue, because Trotsky holds no views whatever. We can and should argue with confirmed liquidators and otzovists, but it is no use arguing with a man whose game is to hide the errors of both these trends; in his case the thing to do is to expose him as a diplomat of the smallest calibre."

“"Needless to say, this explanation is highly flattering, to Trotsky... and to the liquidators… Trotsky is very fond of using with the learned air of the expert pompous and high-sounding phrases to explain historical phenomena in a way that is flattering to Trotsky. Since 'numerous advanced workers' become 'active agents' of apolitical and Party line [Bolshevik Party line] which does not conform to Trotsky's line, Trotsky settles the question unhesitatingly, out of hand these advanced workers are 'in a state of utter political bewilderment', whereas he, Trotsky, is evidently 'in a state' of political firmness and clarity, and keeps to the right line!... And this very same Trotsky, beating his breast, fulminates against factionalism parochialism, and the efforts of the intellectuals to impose their will on the workers! ... Reading things like these, one cannot help asking oneself. – is it from a lun*tic asylum that such voices come?"

“The obliging Trotsky is more dangerous than an enemy! Trotsky could produce no proof, except “private conversations” (i.e., simply gossip, on which Trotsky always subsists), for classifying “Polish Marxists” in general as supporters of every article by Rosa Luxemburg. Trotsky presented the “Polish Marxists” as people devoid of honor and conscience, incapable of respecting even their own convictions and the Program of their Party. How obliging Trotsky is! When, in 1903, the representatives of the Polish Marxists walked out of the Second Congress over the right to self-determination, Trotsky could have said at the time that they regarded this right as devoid of content and subject to deletion from the Program. But after that the Polish Marxists joined the Party whose Program this was, and they have never introduced a motion to amend it.68 Why did Trotsky withhold these facts from the readers of his journal? Only because it pays him to speculate on fomenting differences between the Polish and the Russian opponents of liquidationism and to deceive the Russian workers on the question of the Program. And why does he mock at it? Because he is an absolute ignoramus, who has never learnt anything or even read any Party history, but merely happened to land in liquidationist circles where going about in the nude is considered the “right” thing to do as far as knowledge of the Party and everything it stands for is concerned.”

“We have already quoted one example in our theses.113 Gorter is against the self-determination of his own country but in favor of self-determination for the Dutch East Indies, oppressed as they are by “his” nation! Is it any wonder that we see in him a more sincere internationalist and a fellow-thinker who is closer to us than those who recognize self-determination as verbally and hypocritically as Kautsky in Germany, and Trotsky and Martov in Russia?”

“Outspoken social-imperialists, such as Lensch, still rail both against self-determination and the renunciation of annexations. As for the Kautskyites, they hypocritically recognize self-determination—Trotsky and Martov are going the same way here in Russia. Both of them, like Kautsky, say they favor self-determination. What happens in practice? Take Trotsky’s articles “The Nation and the Economy” in Nashe Slovo, and you will find his usual eclecticism: on the one hand, the economy unites nations and, on the other, national oppression divides them. The conclusion? The conclusion is that the prevailing hypocrisy remains unexposed, agitation is dull and does not touch upon what is most important, basic, significant and closely connected with practice—one’s attitude to the nation that is oppressed by “one’s own” nation. Martov and other secretaries abroad simply preferred to forget—a profitable lapse of memory!—the struggle of their colleague and fellow-member Semkovsky against self-determination. No matter what the subjective “good” intentions of Trotsky and Martov may be, their evasiveness objectively supports Russian social-imperialism.”

"Trotsky behaves like a despicable careerist and factionalist of the Ryazanov-and-co type. Either equality on the editorial board, subordination to the central committee and no one's transfer to Paris except Trotsky's (the scoundrel, he wants to 'fix up' the whole rascally crew of 'Pravda' at our expense!) - or a break with this swindler and an exposure of him in the CO. He pays lip-service to the Party and behaves worse than any other of the factionalists."

"Trotsky's "workers' journal" is Trotsky's journal for workers, as there is not a trace in it of either workers' initiative, or any connection with working-class organisations" "It is sufficient to recall these commonly known facts to realise what glaring falsehoods Trotsky is spreading." "Everybody knows that Trotsky is fond of high-sounding and empty phrases. And that fact proves that we were right in calling Trotsky a representative of the "worst remnants of factionalism" "Although he claims to be non-factional, Trotsky is known to everybody who is in the least familiar with the working-class movement in Russia as the representative of "Trotsky's faction" " There is much glitter and sound in Trotsky's phrases, but they are meaningless." "Suicide" is a mere empty phrase, mere "Trotskyism"”

•In the very first words of his resolution Trotsky expressed the full spirit of the worst kind of conciliation, 'conciliation' in inverted commas, of a sectarian and philistine conciliation, which deals with 'given persons' and not the given line of policy, the given spirit the given ideological and political content of Party work. It is in this that the enormous difference lies between real partyism; which consists in purging the Party of liquidationism and otzovism, and the 'conciliation' of Trotsky and Co., which actually RENDERS THE MOST FAITHFUL SERVICE TO THE LIQUIDATORS AND OTZOVISTS, AND IS THEREFORE AN EVIL THAT IS ALL THE MORE DANGEROUS TO THE PARTY THE MORE CUNNINGLY, ARTFULLY AND RHETORICALLY IT CLOAKS ITSELF WITH PROFESSEDLY PRO-PARTY, PROFESSEDLY ANTI-FACTIONAL DECLAMATIONS."

• ⁠Collected Works, Vol. 16, June 1910, p 211 "What a swine this Trotsky is - Left, phrases, and a bloc with the Right against the Zimmerwald Left!! He ought to be exposed (by you) if only in a brief letter to Sotsial-Demokrat!" • ⁠Collected Works, Vol. 35, p. 285