You should go for the jugular TBH. Ask them why they’re mad that the left takes issue with support for apartheid/ethnic cleansing, building border walls, and the other fascist policies that have bipartisan support; someone going on about “democracy or fascism” like this needs to be forced to answer for why they support these things.

Edit: just saw your edit. My advice still applies. I’d also say that arguing over how far left these politicians are is an irrelevant tangent for the most part. Just make them answer for why they support fascist policy and oppose people calling it out; put them on the defensive and make them try to justify it.