re: If you’re trying to “convert” a leftist

You can't come at cult members like leftists straight on. If they already know you're not on their side, they put up a hard wall. Make them believe you are liberal or at least left leaning. Don't say anything to directly confront their biases. Very mildly un-pc jokes can open a crack in the wall, you have to be careful with those, though. Discussions about being uncomfortable with leftist policies that genuinely hurt, say, women or children (there are plenty of those) can leave them with their own burning questions and thoughts later, just be sure to make it sound like you're confused about it too. The racial idiocy is also a good place to pick at slowly.
Always talk to them alone, never when they are with their group. Many of them are more willing to admit to feeling unsure about leftist thought when alone, they will never break rank when in front of other leftists.