Answer:
It proves he was racist against Jewish people.
Explanation:
For Stalin, whose deeds easily matched those of Hitler and whose deceits had been evident throughout his life, the Doctors' Plot and intended show trial were meant to cleanse the Soviet Union of “foreign,” “cosmopolitan,” and “Zionist” (read Jewish) elements.
The word <em>whom </em>in this sentence is used as 2. object of a preposition.
Since it can be found after a preposition <em>for, </em>it is object of a preposition.
