-you could talk ab his lack of political acumen -> he always preferred to take the 'high minded' approach in terms of political debates (using pen and paper), and did not like to form alliances with others and did not really bother building/consolidating a power base despite having led the red army, ultimately contributed to his expulsion, because well that's not how you really win a power struggle
-bolsheviks were scared of trotsky becoming dictator because of his effective oratory skills
-trotsky underestimating stalin