In just the four years since the last presidential election, cable’s big three -- CNN, Fox News and MSNBC -- have seen a shift. As viewership’s increased, they’ve also risen in prominence and now rival nightly broadcast newscasts.

During the 2004 presidential election, the Pew Research Center for the People & the Press found that for several key demographics, including college graduates and affluent Americans, cable was their leading source for campaign news. They also found cable news trailed only local TV news as a regular source of campaign information.

Since the last election, cable news stories have gained more standing, even taken on a life of their own, as a result of the repetition and constant exposure, and this exposure has been especially noticeable during the 2008 presidential campaign.

Presidential campaign stories don’t have as much impact or become as important to a candidate’s campaign until they get heavy coverage on cable, especially when their story becomes breaking news. For example, the Rev. Jeremiah Wright story consumed cable news’ coverage with an intensity usually reserved for political scandals and celebrity deaths.

Wright was Democratic nominee Sen. Barack Obama’s former pastor and had been typically described as a controversial and ‘fiery’ orator, but it wasn’t until early 2008 that millions of viewers saw just how controversial and fiery Wright could be. Both Fox News and ABC News aired DVDs of Wright’s more inflammatory sermons causing the story to go from brushfire to raging inferno.

By the end of the week, the story was on the Washington Post’s front page, and Obama addressed his relationship with Wright in a speech that aired live on cable.

Cable networks amplify the blunders and missteps in a presidential campaign, and that usually results in days of discussion on programs such as Anderson Cooper 360°, Hannity & Colmes or Hardball with Chris Matthews.

For candidates, cable’s round-the-clock coverage also means that the candidates no longer have to wait until late afternoon to make or break news.

Republican nominee Sen. John McCain responded to the New York Times’ story about his alleged relationship with lobbyist Vicki Iseman at a morning press conference. By the time it was reported on the ABC, NBC and CBS evening newscasts, it was essentially old news.

Cable news exerts its biggest influence on the rest of the media as a catalyst of reaction and response, as cable’s immediate and often intense coverage can magnify an event until that event seems like the only story being covered, which can compel the rest of the media to cover the same story.

All-news channels may not cover many subjects throughout the day, but they do focus intently on one story, e.g., the Persian Gulf War, Sept. 11 or the recent financial crisis. But cable’s coverage of such events can be disproportionate to the rest of the news media outlets, and has potential to distort the public’s perception of the media’s agenda and objectivity.