HARRY HOPKINS WAS THE HIGHEST PLACED SOVIET AGENT UNLESS YOU COUNT FDR

See Stalin's Secret Agents.

He did enormous damage, greater than White, or Hiss, or the others, etc. He ran Lend Lease, etc. favoring Soviets over other so called allies, and sending enormous classified documentation on atomic research to Russia.

It was only nuclear weapons that kept Stalin at bay in 1945, not FDR's alliance.