“And, why does the US ship to the USSR, in the Spring of 1943, tens of tons of nuclear materials - including enriched uranium?”
Interesting, I had never heard that! Where did your read about that?
I know that the FDR administration had its traitors like Harry Hopkins and Alger Hiss, but would allowed that to happen?
Harry "The Hop" Hopkins, FDR's alter ego, was the director of the Lend-Lease program at the time (from VENONA Project and other sources - Hopkins was USSR "Agent No. 19").