Entering the political sphere as a student influenced by Marxism and socialism, he worked as a parliamentary assistant to Hadash MK Meir Vilner.[8]
For the April 2019 Knesset elections, he was placed fifth on the joint Hadash–Ta'al list, and filled the "Jewish slot" after the retirement of Dov Khenin.[12] In March 2019, he was banned from contesting the elections by the Central Election Committee, due to what it described as provocative statements he had made, such as calling Ayelet Shaked "neo-Nazi scum".[7][13] The decision was later overturned by the Supreme Court.[14] He subsequently entered the Knesset as the alliance won six seats. He was re-elected in September 2019, 2020, and 2021.
In April 2021, Cassif was filmed being assaulted by police officers at a protest against evictions and Israeli settlements in Sheikh Jarrah, East Jerusalem. Various otherwise opposing politicians spoke out about the incident, including leader of the Ta'al party, Ahmad Tibi, and right-wing Likud lawmaker Gideon Sa'ar, who described the attack as "a murderous blow to the parliament and to parliamentary immunity".[15][16] Cassif was investigated for striking the policeman first.[17]
On 8 October 2023, Cassif told Al Jazeera that his party had repeatedly warned that continued Israeli occupation of the Palestinian territories would lead to events like the Israel–Hamas war, in which innocent civilians on both sides would pay the price. He called the Israeli government "fascist", and accused it of carrying out pogroms and ethnic cleansing against the Palestinian population.[19] He was later ordered suspended for these comments and others by the ethics panel of the Knesset for 45 days, a decision which Cassif characterised as "another nail in the coffin of freedom of political expression".[20]
On 7 January 2024, Cassif announced his intention to join South Africa in its legal proceedings against Israel brought under the Genocide Convention.[21] Cassif stated:
My constitutional duty is to Israeli society and all of its residents, not to a government whose members and its coalition are calling for ethnic cleansing and even actual genocide. They are the ones who hurt the country and the people, they are the ones who led South Africa to turn to The Hague, not me and my friends.[22]
In response to these comments, 85 Israeli members of parliament (out of 120) signed a petition to expel Cassif from the Knesset,[23] accusing him of treason.[24] The measure came up for a vote on 19 February 2024, with Cassif narrowly avoiding expulsion.[25]
Personal life
Cassif is Jewish, is married, with one son, and lives in Rehovot.[26]