Many jurisdictions, such as DC, have their own fair housing law. These laws often include additional protected classes not found in the Federal Fair Housing Act, such as, inter alia, marital status, gender identity, sexual orientation, age, source of income. DC also protects against discrimination on the basis of political affiliation. In light of this, does refusing to rent to an individual who supported Trump violate this protection? It is not clear-cut. Arguably, it may. However, if the limitation applies only to individuals who are supporters of Trump, a reasonable argument could be made that it does not.
Apparently, this has started to become a reality: people searching for roommates stating explicitly that they do want to live with a person who supported Trump. The NY Times has written an article on this topic.