Caroline Glick has written an excellent article here about how the left abandoned Israel in the 1960’s. The abandonment was facilitated by collaborations between Palestinian groups such as Fatah, and African Americans, as documented in an FBI report linked to in the article.
The article also recognises the stalwart efforts of Martin Peretz to present the pro-Israel side from the left.
Glick, who grew up in Chicago, also describes the anti-Israel milieu that Barak Obama inhabited.
Glick’s article helps to explain links that also have parallels with the left here in Australia, including the rude shock to Jewish Communists when the USSR and socialist groups cut dies with Israel after the 6 day war.