Okay. Since I am going away in a few short weeks and I will be hanging out with a liberal, I am arming myself with tactics. Here is one that I came up with that I think would be very effective if a lib spouts a position that you do not agree with but you just don't have all the facts to rebut him or her. When faced with that situation you respond with this one.
"My gut reaction would be to disagree with you on this point, but I have to confess I do not know enough about your position... do you mind if I ask you a few questions?
What I like about this is that you are not only civil, you are also relieving some of the pressure from yourself in thinking you have to know everything. Now after you make that statement, you ask them some probing questions, the object being to lead them to your turf which in my case would be getting at their core beliefs. With that said, you need to be prepared for them to throw curves at you, such as them implying you are racist. Here is what that exchange would look like.
My gut level reaction would be to disagree with you.
Is that because you are a Racist?
You would then pause and reply: Well, unfortunately this discussion has taken a turn for the worst in that I just found out I am dealing with an ill mannered creep.
Here again, I am riffing off of Ben Shapiro in that you do not have to put up with those insults. Again, don't try make this a teachable moment. Once you have been insulted your focus becomes the projection of strength and you do that by speaking to them in way that they only understand. which is to get right back in their face.
Hopefully it won't get to this point and you can continue with the original plan which is to ask questions. So, I hope this helps. Happy Trails!