Should a political representative use his vote to represent the people or vote what he believes is right and best?

We vote for our congressmen to represent what we the people want. I was thinking about this because I was talking to a friend of mine about how Harold Ford, now running for a senate seat in NY, is pro gay marriage, but when he was in TN wasn’t (athough he was for same sex civil union). Many have said that he changed his stand to be able to get elected, that he lacks integrity, but I guess you could look at it like he changed his “opinion” because it better represents what the electorate desires in each of the states. We have seen many politicians do this. I know many will say it is just politics and they are just doing whatever they have to do to get elected, but maybe a small part of it has to do with representing the people?

Once elected what if a topic comes up that was not even really spoken about during the election process? Should a representative completely ignore emails, phone calls, and letters sent to him, trying to pursuade him to vote a certain way? Or, should he go only with his own evaluation of an issue?