“[I]n politics, sincerity isn’t as important as results.” (Source)
I don’t care (much) about a politician’s personal preferences, or his historical votes, I care about how he votes on the next vote. The voting record has some predictive value, certainly, and statements from the politician should be taken into account; but the secret of the universe is, things change, people change. Politicians change because people change. If they don’t, they get voted out of office, or don’t get elected to higher office.