Most politicians start off in life with excellent intentions of doing good.
However it is necessary to get on with senior politicians, and in Party system do what the Party wants. From then on it is usually a slow job climbing the ladder. So their first loyalty is to the power brokers in their party and their second loyalty is to their electorate. Politicians out of power are not very effective so that they have to do everything to get in and remain in power. In many countries we see how the top man often gets rid of the opposition by imprisonment or assasination.