In politics, it's the "juice" that the leader of a political party has in a election victory - his/her popularity adds a boost to many other candidates, often meaning the difference between defeat and victory. At worst, it results in the "look what the cat dragged in" syndrome - officials who shouldn't have been elected dog catcher, e.g. the Upper Class Twits who rode in with Margaret Thatcher, or some in the current crop of Republicans, beneficiaries of Newt Gingrich's 1994 upset.