[ptaipale]

I would call this "the risk of divided loyalties". If you spoke a foreign language, if you had relatives abroad, if you had been born abroad, if you had a distinct ethnicity, if you had a religion, if you had neighbours or friends who had anything of the above.

Any of these would make someone think that you might be disloyal to the Soviet state and loyal to something else, and therefore increase your likelihood of being arbitrarily picked up for espionage, treason or sabotage charges. And once picked up, the guilty one had been arrested, because the system does not make mistakes. At this point, it's only the crime that needs to be found.

(It is attributed to Stalin that he said "there are no innocent people, only people who haven't been properly investigated yet." Not sure if he actually said this anywhere.)

The risk of Jewish people having shared loyalties to Israel is mostly a post-1948 thing of course so it was in a different form during the Great Purges.

[_delirium]

Fwiw this used to be a major concept in American political discourse as well, regarding both Jews and Catholics, although it typically didn't extend to actually arresting people, just keeping them out of political positions, and "sensitive" employment like schoolteacher. There was a widespread opinion that they had "divided loyalties" because while they were Americans, they also might feel loyalty to (depending on who you asked) foreign leaders or movements like the Pope or "International Jewry". The first serious Catholic candidate for U.S. president (Al Smith in 1928) was widely accused of being unfit to be U.S. president because his religion meant that he had a religious obligation to follow the infallible guidance of the Pope, a foreign head of state.

[ptaipale]

Quite. I suppose the interment of Japanese Americans in 1940's is a prime example of this. Later it has been widely denounced.