it says in the Torah (I'm quoting from Gentiles in Halacha btw):
it is written in the Torah (Deuteronomy 17:15): “Then you shall appoint a king over you, whom the Lord your G-d will choose: one from among your brethren shall you set as king over you, but you shall not set over you a stranger who is not your brother.” In Sifri, Shoftim, paragraph 157 it says: “Your brother, and not from others” (that is to say, Gentiles, for a Gentile king may not be appointed over Jews — Rabbeinu Hillel). And not just a Gentile, but also a righteous convert, considered a Jew in every matter, is disqualified for kingship, as is explained in Midrash HaGadol: “‘You shall not set over you a stranger ‘ — to exclude the convert… from here they said it is forbidden to appoint a king from the converts, even after a number of generations, until his mother is [one born] Jewish.”
This is also the law concerning any position of authority, as explained in Kiddushin 76b: “We have learned: ‘Then you shall appoint a king over you from among your brethren,’ all appointments of authority that you make should not be[made] except from among your brethren.” Thus wrote Maimonides in chapter 1 of The Laws of Kings, halacha 4: “We do not appoint a king from amongst the converts, even after several generations, until his mother is [one born] Jewish, as it is written, ‘You will not set over you a stranger who is not your brother.’ Not only for kingship, but also for any position of authority in Israel (?), neither a general nor chief over fifty people, nor chief over ten people, nor even a person appointed to verify that the water is distributed to the fields. It is superfluous to talk about a judge or a nasi, who may not be other than [one born] a Jew, as is written, ‘one from among your brethren shall you set as king over you’–all the people whom you give positions of authority shall not be from other than your brethren.”
The only questionable part is when it says, "...Not only for kingship, but also for any position of authority in Israel..", is this only talking about a ruler in the land of Israel, or does it mean a position of authority over the people of Israel (wherever they may be)?