A politician is an individual who is usually campaigning for some type of elected post (i.e., Mayor, president, city council). In order to win the post, the poiltician must recieve the majority of votes in an election. Votes are cast by citizens, so the main objective of the politician should be to find out the needs of the majority of the people. This is achieved through campaigning. Campaigining is the process the politician uses to meet citizens of the community of the post they are running for. Campaigning usually entails the politician speaking at community events, hosting events, making speeches, etc, to promote their platform.
The platform is the foundation of the politician's campaign. Usually a platform consists of a hot-button issue that is currently developing or has developed in a community. The politician decides his platorm, which issues he or she will and will not promote, etc, and his or her personal thoughts on said issues.
Campaigning and platform are usually the deciders in a political election. Obviously, the better the campaign, the more voter approval. If individuals believe in what you belive in, they will usually vote for you (platform), but you have to reach the intended audience (campaign).
Sometimes, politicians will use campaigning resources to try and discredit any opponent they may have in the electoral race. This is commonly referred to as mud-slinging. Politicians may air commercials portraying thier opponent in a negative manner, or may even say negative things about their opponent during their campaign speeches. Often, this has an adverse effect, as it compromises the integrity of the politican in the eyes of many voters.
Politics and politicians have suffered from an increasingly negative image throughout the years due to scandals involving bribes, sex, and crime. This can occur at any level of politics, but the most sensationalized cases are usually at a national level (president, vice presidents, senators, representatives, supreme court justices, etc.). This is likely due to the fact that these individuals are scrutinized much more closely by the media.