Actually I do believe a fair number of politicians enter the arena with good intentions (though often without realizing how interconnected and difficult the realities are) only to be told in the back room that they cannot do what they wish because that's not how things work. Furthermore, if they want to keep living they'd better do what the "real bosses" tell them to do. In the US, those bosses are a few hyper-wealthy and completely unscrupulous individuals.