They call it Political Monogamy, but I prefer the more precise term, Demisexuality. The abominable practice is every bit as stupid as Vegansexuality. I always suspected that an unusually high percentage of male Democrats were Demisexuals.
I must admit, to my lasting shame, that I often posed as a 'leftist campus radical' in my college days. Their parties were wilder and the women were more fully liberated (read: easier) than their non-leftist counterparts. It was less trouble than lying to the ladies about being rich or ambitious.