After watching the UK Labour party go through this for the last 30 years (technically longer but not in my political activity) which is a far less robust and more easily coopted party than the dems I'm inclined towards the position that entryism in the dems is a totally futile endeavour bordering on harmful because if they get a small amount of success you will end up locked into a socdem vs conservative political battle for 30 years that eliminates any possibility of socialism until some stupid ass neoliberals find a way to purge the left as "antisemitic" and inadvertently causes a whole new left movement.