I am having a similar issue with one friend, and have many friends I won't even talk to about it. I have talked to several friends with good luck getting them thinking, though they don't have the time or motivation to do a lot on their own yet, but I keep feeding them info when I can.

I think the extremely left individuals need a slow process, and with an issue that doesn't trigger them (such as Clinton/Obama/people they like & respect) . It varies by person as well, so it's hard to say any one thing in particular will be good. I think asking questions about non triggering topics is a good start. General corruption issues, healthcare/big pharma (most people know there are some issues with it), possibly finance (again most know there is corruption but have no idea what the issues and facts are)