Histadrut: Israel's racist "trade union"
As unemployment grew in the Zionist economy in Palestine in the 1920s, Histadrut launched a campaign to promote Jewish labor (Avodat Ivrit) and Jewish produce (Totzeret Haaretz), which was essentially a boycott of Arab labor and produce. David HaCohen, former managing director of Solel Boneh, described what this meant:
"I had to fight my friends on the issue of Jewish socialism to defend the fact that I would not accept Arabs in my trade union, the Histadrut; to defend preaching to housewives that they should not buy at Arab stores; to defend the fact that we stood guard at orchards to prevent Arab workers from getting jobs there ... to pour kerosene on Arab tomatoes; to attack Jewish housewives in the markets and smash Arab eggs they had bought ... to buy dozens of dunums [of land] from an Arab is permitted but to sell God forbid one Jewish dunum to an Arab is prohibited; to take Rothschild the incarnation of capitalism as a socialist and to name him the 'benefactor' -- to do all that was not easy." 
In 1944, "the mere rumor that a cafe in the exclusively Jewish town of Tel Aviv had taken on a few Arab workers provoked an angry gathering of thousands of demonstrators. ... Every member of the Zionist Trade Union Federation -- the Histadruth [sic] -- had to pay two compulsory levies: (1) 'For Jewish Labor' -- funds for organizing pickets, etc. against the employment of Arab workers, and (2) 'For Jewish Produce -- for organizing the boycott of Arab produce.'" 
It was Histadrut which mapped the route the Zionist project would take in Palestine. From the start it excluded the Palestinians, first from the economy and later from the land itself. Class struggle was redefined as the struggle against Arab labor, as Ben-Gurion railed against "the evil of mixed labor"  Ben Gurion explained to those who mistook Histadrut's red flags for socialism that "Nothing is further from the mind of Jewish labor than to engineer disputes with all the material and political loss in their train. For it, the supreme charter of our generation is reconstruction and Aliyah [immigration to Palestine]. ... It is a charter meaningless without Jewish labor."  With typical colonial condescension, Ben-Gurion spoke of Arab workers acquiring "a smattering of culture" through mixing with Jewish workers. 
From almost the very beginning of political Zionism, certainly, from the early 20th century, Zionism has been about racial apartheid and Jewish supremacism. Those are still the essential characteristics of Zionism and the Israeli state.
The reason why the likes of Bernie and Frank resort to bullying and suppression of free speech in response to Palestinian solidarity organizing, and why the tactics used by "volunteers" of pro-Israel lobby groups in their pressure campaigns often include blatant lying and deception, is that they cannot win an open debate on the issues with facts and ideas. Because the facts are clear. Israel is, and always has been, an apartheid state, born out of the violent and meticulously planned ethnic cleansing of Palestine. That can never be defended by appeals to ideas of justice and equality.