stemmerist
A stemmerist is an individual who advocates for or practices "stemming." Stemming is a technique, most commonly associated with Russian revolutionary politics, that involves actively participating in and seeking to influence established political parties or movements from within. The goal of a stemmerist is often to steer the direction of these organizations towards a more radical or revolutionary agenda, rather than forming separate, independent radical groups. This approach contrasts with outright party-splitting or the creation of entirely new political entities.
The term and practice are often linked to the Bolshevik faction of the Russian Social Democratic Labour