Extremely partisan talk-radio/TV commentators have a lot of influence.
Also, consider standard print and online publications, most of which emphasize the news and commentary that agrees with their points of view.
Online social networks and forwarded emails also spread specific points of view.
one more question. what critical thinking skills can help with making careful voting decisions.
Watch and listen to MANY different sources of information, not just one or two. Then consider everything before making decisions.
All of the critical thinking skills you're learning will help you make careful voting decisions. Read and listen widely and critically. Check facts. Recognize sheer propaganda.
These sites make interesting reading on this topic.
One of the ways that bothers me most is that TV media are focused on short sound "bites"...which often do not reflect the candidates thinking, but reduces complex issues to idiotic simple slogans: no new taxes, coporate jets, drug free America, hard on crime, choice, don't kill babies, Love waits pledge, and so on. This is the way to not critically think, form a slogan, and assume all agree on what it means.