Was Abraham Jewish?

Rabbi Blass, Someone asked you if Ishmael was Jewish, and you answered "no". Isn’t it true that Isaac wasn’t Jewish either? In fact, isn’t it true that Abraham wasn’t Jewish? Didn’t Abraham’s grandson Jacob (Israel) form the nation of Israel through his twelve son’s, and the descendants of the southern nation of Judah and Benjamin become known as the Jews, and the descendant’s of the northern nations became known as Israel?

The patriarchs were not "Jewish" in the sense of having accepted the Torah at Mt. Sinai since they lived before the giving of the Torah. However, they were not "non-Jewish" inasmuch as they were "Israel- in- the- making". Chazal (see for example Yoma 28b) teach that the forefathers kept the mitzvot even before they were given- which mitzvot, where (only in Israel or also outside of Israel), in what form- is a question debated by the rabbis over the generations: see Maharal Tifereth Yisrael ch. 19-20 and Sefer Parashat Derachim of the Mishne L'Melech who discusses at length to what extent the patriarchs conducted themselves as Jews. Ishmael was outside of this tradition.