A leftist coalition organized against a common opponent WordNet 3.0 & Open English WordNet

A popular front is "any coalition of working-class and middle-class parties", including liberal and social democratic ones, "united for the defense of democratic forms" against "a presumed Fascist assault". Wikipedia

Term for a political coalition which is commonly made up of parties ranging ideologically from liberalism to communism, historically for the purpose of opposing the rise of fascism or far-right politics in general. In Post-Soviet states, the word has a different meaning, instead connoting a liberal intellectual organization formed to support self-determination for the territory in which it operated. Wikipedia Disambiguation

Broad political alliance between leftist and centrist parties Wikidata

A broad coalition of different political groupings, usually made up of leftists and centrists. Wiktionary