I've dated a hardcore lefty before.

She was cute and we could make each other laugh when we weren't talking anything serious, that was pretty much the only thing keeping me going. Shallow, but it's the truth. We rarely got into discussions on political philosophy and it was always her instigating it (why open Pandora's Box when you already know what's inside?). But when we did it genuinely felt like I was talking to someone that lacked even a basic understanding of the topics, events, people, etc. - she couldn't even list the then sitting justices on the Supreme Court, never mind actually knowing each of their own leanings, beliefs in how the Constitution should be interpreted, rough voting record, etc. After one discussion she once told me that I was "probably the most well read Trump supporter she's ever talked to" and I replied "I'm guessing you don't talk to a lot then, because there are many many many more out there with a better understanding of all of this stuff than me and they could probably give better answers than I could." It really dawned on me then that people like her genuinely don't attempt to ever see the other side, talk with people of differing views, to ever remotely have a simple understanding of their philosophies (at least not with a sincere attempt to understand them and with an attempt to be open minded). It's essentially "I'm right because I just feel I'm right and I don't want to put in the effort to understand how I could be wrong."