It's normally a safe assumption to make, but not always. Some of my left leaning customers sometimes assume I'm a Democrat because I'm black. Makes for some awkward situations.
Many,many people in my life assume I am a lib. I love my hairdresser and when she makes rueful jokes putting down the President I think of her lovely way with my hair and my kids’ hair and shut the heck up. Everyone at my kids’ schools too, I stay in my closet.
My friends know, and tolerate (even love!) me in spite of my politics. My extended family knows and they treat me with just the etiquette-allowed amount of disdain. Almost like I was a real person, you know what I mean.