Something that is drastically shaped by its audience are news channels. People tend to watch whichever news channel appeals to them most and corresponds with their political views, especially in America. One example is Fox News. The overwhelming majority of the time, conservatives are the ones who tune in to this channel, while liberals are more likely to tune in to CNN or NBC News.
These channels have specific target audiences in mind. They talk about stories that the audience will want to hear and affirm their beliefs, not contradict them. This article from Business Insider talks about bias in the news channels in America. http://www.businessinsider.com/what-your-preferred-news-outlet-says-about-your-political-ideology-2014-10?IR=T
This issue is unlikely to ever go away, but is a fact of the media. However, it causes and feeds into a lot of issues regarding politics in America. If people only listen to one news channel, and that news is all biased, they really only hear one side. As a result, Americans are not fully educated on issues and do not have a very open mind when it comes to politics. If all they hear is something that just re-affirms their own beliefs, they will not hear any other opinions. Media bias as a result contributes to the polarization of political affiliations in the country; Democrats versus Republicans.