The soviet objective was to humiliate GB. A few years later, they were the first, via Czechoslovakia, to arm Egypt in defiance of the Tripartite Agreement.
Stalin was vicious in his anti-Jewish attitudes. I think political calculation, personal grudges, family incidents and just a lifetime of being a mass murderer was producing a leader who would have made the hardest czar in history look like Barney the Purple Dinosaur. The Doctor’s Plot was going to be the crowning achievement of a sick life.