As far as the Communist Party of the Soviet Union was concerned (as well as its predecessor, the Bolshevik Party), Jews were a minority.
They were well-represented in the higher echelons initially, true, and socialism and the way of the narodnik may have been an appealing alternative to Zionism for the average Jew in Russia, but they were quite the minority within Party ranks.
Russians formed the majority -- 60% in 1917, IIRC -- and that only increased as time passed.
