I know that Stalin was only one of several successors to Lenin (and not a favored one at that) when Lenin died. However, Stalin was able to quickly forge alliances within the Party to oust his most powerful rivals (Trotsky, Zinoviev, and Kamenev) and establish control of the USSR. Even Bukharin - a former ally - was expelled in 1929. Stalin banned Party factions, removing official voices of dissent.
And yet he still felt the need to have all his disgraced and defeated opponents put on trial and murdered. He then proceeded to purge other prominent Communists (as well as many ordinary people).
Did Stalin face any resistance to the Purge politically? Was there anyone powerful enough left after Stalin's rise to power but before the Purge began, or was Stalin completely "punching down"? I am interested in the political figures, so while "such and such general controlled so many million troops" is potentially interesting, the general would also need to be somewhat politically active to merit a mention.