Best topics for that kind of person are the ways the liberal framework screws over normal people in favor of the bourgeoisie - how it actively worked against things that person specifically advocates for. An example from my own life was back in 2009 when I realized that Obama wasn't going to inflict any repercussions on the banks that defrauded people until the economy collapsed while my friends were evicted from their houses. You'll have to tailor the argument to where you live and whatever their key issues are, climate change is usually a safe bet for that kind of person but they might have something else.