Go to facebook.com/ads/preferences on your browser. (You may have to log in to Facebook first.)I've never "liked" any political candidate or political party or political cause on Facebook. According to Facebook: "You have this preference because we think it may be relevant to you based on what you do on Facebook."
That will bring you to a page with your ad preferences. Under the “Interests” header, click the “Lifestyle and Culture” tab. Then look for a box titled “US Politics.” In parentheses, it will describe how Facebook has categorized you, such as liberal, moderate or conservative.
(If the “US Politics” box does not show up, click the “See more” button under the grid of boxes.)
Facebook makes a deduction about your political views based on the pages that you like — or on your political preference, if you stated one, on your profile page. If you like the page for Hillary Clinton, Facebook might categorize you as a liberal....
Even if you do not like any candidates’ pages, if most of the people who like the same pages that you do — such as Ben and Jerry’s ice cream — identify as liberal, then Facebook might classify you as one, too.
August 24, 2016
From "Liberal, Moderate or Conservative? See How Facebook Labels You" (in the NYT):