Rav Lior quoted Rav Kook as saying that the Erev Rav are Jews who support our enemies. This would definitely fit the NK and their fellow travelers. According to Rav Yehuda Ben-Yishai they are those who doubt Hashem’s ability to bring about the Geula. There are also the Spies, whose sin the Gra (quoted in “Kol HaTor” and “Em HaBanim Semeicha”) says will infect many who who hold on to the Tora. They oppose yishuv EY – many times for “frum” reasons. See Baal HaTanya, Likutei Tora on parashat Shelach 38b:
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