Communist parties lost credibility by abandoning independence for nationalist alliances. [causal]
In the 1960s, the CPs once again switched position to accommodate Soviet directives. The CPs of Syria, Lebanon, Iraq, and Jordan issued a joint statement in 1964 calling for "closer unity and cooperation between all the patriotic and democratic trends and . . . all the national forces of the Arab liberation movement." In practice, this meant that the Syrian CP declared the Ba'ath Party one of the "basic revolutionary forces." The Syrian Communists then entered the regime and gave up all political independence. Similarly, the Iraqi Communist Party aligned itself with the Ba'ath Party and, by association, the war against the Kurds and the repression of Shi'a Muslims. All of these disastrous shifts delegitimized the CPs in the eyes of people who had once turned to them for leadership. Additionally, the parties' uncritical support for various "revolutionary" nationalist parties and regimes meant that when radical nationalism went into decline, the CPs too suffered a loss of credibility.
XREF: Pattern mirrors Soviet-aligned parties globally abandoning independent positions in the Cold War era.
Deepa Kumar, Islamophobia and the Politi…, loc. 336