You make your base bigger BY playing to it.
The losing strategy is to move to the right, to assume with Republicans that American values are mainly conservative and that the Democratic party has to move away from its base and adopt conservative values. When you do that, you help activate conservative values in people’s brains (thus helping the other side), you offend your base (thus hurting yourself), and you give the impression that you are expressing no consistent set of values, which is true! Why should the American people trust somebody who does not have clear values, and who may be trying to deceive them about the values he and his party’s base hold?..."No Center, No Centrists" -- George Lakoff
http://www.commondreams.org/archive/2007/08/15/3174 NGU.