You can find out.
Go here: https://www.facebook.com/ads/preferences
Then click on the Your Information box, which should be like the 3rd one down.
Then within "Your Information", click on "Your categories".
Look for a box in there which says "US Politics", and it will say how it rates you.
For me, it says "US Politics (very conservative)".
Much of this is based upon posts you share and groups you've joined, but it also uses keywords in your own posts to determine this.
Facebook collects this information for advertisers, so they can target ads according to your political leanings.
It also rates me as a "Frequent Traveler", presumably because I log into Facebook from many different secret locations.