I'm going to attempt to say this in a way that reflects my beliefs on this situation, without offending anybody.
Here's my take:
First of all, this happened a month ago. Not saying when it happens has anything to do with the ethics of what was being said, but it brings into question the validity of this report. Not only does it taint the chances that this report is being made for the right reason, but your excuse for it not being brought up earlier is what I would like to call a "cop out". If his comments offended you to the degree that is being implied with this report, you would have reported it right away. I don't really understand the whole "blackmail" or "harassment" worries because if something like this is truly wrong, there would be no reason for people to "harass" you about complaining about it. If there's something I don't know about, then please inform me, however the only reason I could see you holding this information back for so long is for personal gain.
Secondly, I don't even think we have all the context on this situation. If you would like to share the DMs you and him exchanged before and after this conversation, I would love to weigh in on those.
Thirdly, I don't find his comments blatantly racist. Based on the screenshots provided, the only thing I can see that would be "questionable" would be his comment where he said racism was a result of "the black race". Even with that statement, while not politically correct, it is not racist. Racism , per the Merriam Webster Dictionary Definition is "a belief that race is the primary determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race". In basic terms, that means holding the belief that one race is superior to another, or a race is inferior than the rest. This is not what he was saying. I'm not saying what he said was right, or that I hold the same belief that he does, what I'm trying to do is see it from both perspectives.
Fourthly, what this really seems like it is to me, is two people from the complete opposite side of the political spectrum going at each other. If you've ever been on twitter, which I'm sure most of you have, you see this kind of thing all the time. You two clearly have extremely different viewpoints on the world, and neither of you are right or wrong. Neither of your worldview's are "correct" because politics is not that black and white. This is so obviously just someone from the far right, arguing with someone from the far left, and while some of the comments made were insensitive and possibly hurtful, they are his beliefs.
With that being said I'm not going to leave a +support or a -support on this post, because all I am attempting to do with this is bring more perspective into this situation. You can read my thoughts and form your own opinion based on all the information provided on this report.