Trotsky in years between 1903-1917 usually tried to position himself between bolsheviks and mensheviks. He also tried to portray himself as mediator between the two but he usually (not always) sided with mensheviks. Needles to say Lenin was not fond of such wobbly political stance and greatly distrusted and often criticised Trotsky. In 1917 Trotsky finally joined bolsheviks and proven his organisational talents, he also came under the political influence of Lenin so the relations warmed, although Lenin still distrusted him. Ultimate colding came with Brest treaty where Trotsky basically sabotaged it and Lenin was furious at him, at this point he never trusted Trotsky again.