It is a journalist's job to bring the news to the public but it should be presented without being influenced by their personal opinion. They are obliged to tell the truth and remain independent from the event being covered. This is fine in theory but in practice how often are the news people or the publications or networks they represent impartial?
Some people believe that political news is always biased depending on the source of the information. For example certain individuals will only believe what they hear on Fox news and not CNN, while others prefer CNN. Some people believe that Fox leans to the right while others maintain it just provides the news in a format that suits their listeners. At the end of the day, it is a matter of education. You should try to obtain information from a variety of sources so that you can form your own educated opinion on current events. Political news will often be controversial. Good news never sold newspapers or increased ratings!
But the people reporting political news should let the facts prove the point. They shouldn't be tempted to stretch the truth particularly if the reason for doing so is to improve ratings. But this is a theoretical argument. In a society where the news stations with better ratings are more successful and thus earn more money, it is probably unrealistic to expect them to remain totally impartial to events happening in political waters.