Liberal tended to belong to the

Liberal tended to belong to the upper middle class.

The upper middle class is the social group constituted by higher status members of the middle class. In the U. S. upper middle class is defined taking in consideration indicators such as education, income, and occupation. They are basically white-collar professionals with above-average income, a graduate school degree, and are characterized by adding value for their thoughts and proposals. Liberals are considered upper-middle-class professionals and were the base of the neoliberal economic and political programs of Bill Clinton and Barak Obama.

Depending on the time period and the context you are referring to, the answer could vary significantly. In present times, liberals tend to belong to the middle or upper-middle class.

This means that liberals in general share some characteristics. They tend to have a higher degree of education in average than conservatives, with many of them attending post-secondary education. They also tend to be wealthier, and to live in urban areas. Finally, liberals also tend to be younger in average than conservatives.