It's called "The Law of Curvilinear Disparity", and you're unlikely to have heard of it unless you're a psephologist. It's a theory, from political scientist John May, that both the elites of political parties and the voters who support it are more centrist than the party membership, which skews significantly more radical.

The experience of the Liberal Party in recent years suggests the party's base -- elderly, and middle and high-income -- indeed skews dramatically more conservative than the electorate as a whole on issues like climate change and 18C and support for Tony Abbott. There are, however, other areas such as same-sex marriage, and the differences have diminished over time; on some issues like support for renewable energy, euthanasia or distaste for privatisation, there appears to be little evidence of noticeable differences between any voters.