Fox News' effect on our political culture extends beyond the network's daily cavalcade of ideological and partisan attacks. Its 15 years in existence and nearly 10 at the top of the cable news ratings food chain have ushered in an era of ideological polarization and post-truth politics.

In the middle of the last decade, there were discussions about the impact of citizen journalism conducted by bloggers and its effect on the media. Under the radar, Fox was using its platform and a major cable news channel to contort our political dialogue, creating two Americas and two truths.

As a political consultant, Fox News President Roger Ailes specialized in dividing voters along racial, ethnic, and religious lines. While working for the George H.W. Bush campaign, he told a reporter, “The only question is whether we depict Willie Horton with a knife in his hand or without it,” and produced the divisive "Revolving Door."

Ailes used these same tactics on Rudy Giuliani's unsuccessful 1989 campaign for mayor of New York. He was criticized for utilizing a strategy that "prey[ed] upon the fears of the Jewish community."

While Fox has certainly stoked racial fears, pushing bogus, concocted smears in an attempt to connect Barack Obama to the New Black Panther Party, it has also created an environment in which truth, facts, and science no longer are paramount. Fox-created facts rule the day. And its viewers trust the network more than any other source. Climate change? Doesn't exist, according to many on the network. Forget what scientists say. Also did you hear that this “climategate” scandal debunked the entire notion of global warming?

Now as a progressive, I will point out that there is overwhelming consensus among scientists that the Earth is warming. Additionally, "climategate" did nothing to debunk the body of scientific knowledge backing up that claim. However, no amount of evidence presented will convince Fox viewers otherwise. Any presenter not fitting the network's worldview is biased, bought off, stupid, or evil. Stephen Colbert astutely pointed out this worldview at the White House Correspondents' Association dinner when he noted that “reality has a well-known liberal bias.” While a laugh line, the outcome of the post-truth era is dangerous: a country not only divided by ideology, but divided along factual lines. Without a common narrative, constructive debate is simply impossible.

This truth dichotomy extends beyond climate science.

In the period before the passage of health care reform, the network chose to highlight the absurd claim made by Sarah Palin that the bill contained death panels. Fox continued to repeat this misinformation to its audience for months even after it had been debunked.

Attending the rally on Capitol Hill the weekend prior to the health care vote, I spoke to people in the crowd. I went around asking a simple question: “Why are you opposing this bill?” Almost universally, the answers I heard could be divided into four catagories:

• Death panels
• We won't be able to choose our doctor under Obamacare
• It is socialism
• It will add to the deficit

Never mind that the death panel had been named the lie of the year by the nonpartisan, Pulitzer Prize-winning PolitiFact; that the plan did nothing to alter people's choice of doctors (that role was already filled by private insurance companies); that the bill, according to the Congressional Budget Office, actually reduced the deficit. Each speaker who appeared on stage, many of whom were frequent guests on the network, repeated more lies to the audience. It's no surprise that when polled, Fox viewers are consistently misinformed on a variety of issues.

Conservative David Frum spelled out the damage when he wrote: “There were leaders who knew better, who would have liked to deal. But they were trapped. Conservative talkers on Fox and talk radio had whipped the Republican voting base into such a frenzy that deal-making was rendered impossible. How do you negotiate with somebody who wants to murder your grandmother? Or -- more exactly -- with somebody whom your voters have been persuaded to believe wants to murder their grandmother?”

As Frum told Nightline in 2010, “Republicans originally thought that Fox worked for us, and now we are discovering we work for Fox.”

The network's impact can clearly be seen in public opinion polling. When Republican polling outfit Public Opinion Strategies -- in a survey conducted for the League of Conservation Voters asked, “Do you support or oppose the U.S. Environmental Protection Agency requiring reductions in carbon emissions from sources like power plants, cars and factories in an effort to reduce global warming pollution?” The crosstabs spelled out the effect Fox has on its audience. Seventy-one percent of Americans supported EPA action. Even a majority of Republicans, 54 percent, were in support of these regulations. However only 49% of Fox viewers agreed.

Fox uses its dedicated audience to create its own truth when the facts simply don't align with its preferred outcome. In its privileged position as the highest-rated cable news network, Fox can easily inject lies into our political bloodstream. While this misinformation is most dangerous when it metastasizes, it can never be filtered out entirely. That is how for 15 years, Fox has fundamentally damaged our democracy.