Some rather unfortunate examples there, Peter.

While the PCF's support for the government of Mitterrand and Mauroy was reasonable-seeming, it resulted in the start of the steady decline of the PCF as a political and social force.

The support of the Tudeh Party for the mullahs lead to the purging and murdering of communist cadres (notably the Tudeh Party no longer supports the mullahs' regime).

Similarly the Iraqi CP's support for the Ba'athists lead to purges and murders in the 1970s of Iraqi cdes.