Far and away the greatest enemies Israel faces are Jews.
Israel Shamir is a very interesting case. He states that he is a Jewish person of Russian ethnicity, who went to Israel, served in the army, and became disenchanted. He later was actively anti-Zionist and converted to Christianity.
OK. That’s the story. But the reason I say “he states” is that there is a claim that he was never Jewish, and that his entire story of his life in Israel is a fabrication, and that he always was a member of the Eastern Orthodox Church.
It is very strange. A fake identity is quite possible (google “Norma Khouri” if you don’t believe me) but definite proof seems lacking.