According to an amazing new "handbook for Progressives," swing voters are made up of "biconceptuals" - people who hold a mix of left and right viewpoints. There are few, if any, true "moderates." That means we should be speaking to the center
in the same language we speak to our base.
The book is "Thinking Points," by framing guru George Lakoff and the Rockridge Institute. It's available at your favorite independent bookseller for just $10. In particular, read "Chapter 2: Biconceptualism," which you can download free here:
http://www.rockridgeinstitute.org/thinkingpointsNGU.