Leftists cannot practice Entryism in the Democratic Party, due to its structure. The DNC is a machine used to filter out radicals and protect pro-establishment politicians that secure the funding from donors the DNC needs to exist. It is not a Leftist Party, and cannot be a Leftist Party.

Secondly, the concept of "brainwashing" is flawed. The ideas people find acceptable are determined by their social consciousness, as Capitalism deteriorates and Imperialism begins to crack, workers are increasingly turned towards organization and revolutionary Socialism.

I highly recommend reading Reform or Revolution by Rosa Luxemburg, she put to pen why reform is a sisyphean task. Reading theory really needs to be taken more seriously.