Well, let's get on with changing some attitudes.
When the slave tradewas banned in Britain, one of the biggest hurdles, as I understand it, was getting the British public to change their minds on it. It's economically lucrative, the victims are "uncivilised" people (who, let's be fair, were selling their own into slavery), and those that want slavery to continue shape the messaging into feeling like slavery is okay business. Getting that changed involved showing the British public just how horrendous the slave trade conditions were.
If you want a United America against fascism, you've got to work on showing Republicans the reality of the corruption, without dismissing them as "uncivilised". It takes time, but grassroots is where to start.