I think you've done good, and I think at least most of us have been in a similar position as you or even in the position of your liberal friend. Most people however dont change their minds on a dime especially when theyve invested so much of themselves into a position and defined themselves by that position. Unless your friend continues to surround himself in the media and refuses to think about what you said, how you got him to think, then that seed of an idea you planted will take root, and it will bear fruit, just not for a while.
It also seems like your friend is operating under some form of chauvinism e.g. American Exceptionalism, so in any future conversations with your friend I'd maybe do some research on arguments against this, Parenti in Blackshirts and Reds helped stamp out the last of that for me.
We have thoroughly investigated ourselves and found no evidence of wrongdoing
Bugs Life