Blame the liberal media.

Its been a regular Republican talking point for over 40 years, ever since Vice President Spiro Agnews criticism of the media as the Nattering Nabobs of Negativism. Now its Donald Trump s main message.

Trump has recently attacked the mainstream media as being unfair, dishonest, disgusting, corrupt and crooked in its coverage of him. He has referred to them as the lowest form of life, to the delight of his cheering crowds. Many people in the crowd now boo the members of the press during Trumps events and chant Lock Them Up. In the past year, Trump has blacklisted and revoked press credentials for many media outlets, including the Washington Post, Huffington Post, BuzzFeed, Des Moines Register, Univision and Politico.

Its ironic that Trump is bashing the media, in that it was the positive and ubiquitous media coverage that helped him dominate the Republican primary field. Trump is now biting the hand that fed him ever since he went down the Trump Tower escalator last year to announce his candidacy. During the primaries, most of the media coverage of Trump was positive. They pretty much ignored the other 16 Republican candidates and let Trump suck all of the oxygen out of the room. The provocative, entertaining and controversial Trump was great for TV ratings. How many Rick Perry, Rick Santorum, or Lindsay Graham campaign events and speeches were televised?

Now that the primaries are over, the media still gives Trump extensive coverage, but it has subjected him to intense scrutiny about his record that did not occur during the primaries.

As I note in my new book, Skewed: A Critical Thinkers Guide to Media Bias, the Republicans complaints about liberal media bias are overblown and over exaggerated. Reporters are trained to be fair and balanced (not the Fox News kind), impartial, neutral and detached. The Society of Professional Journalists (SPJ) Code of Ethics emphasizes that reporters should seek the truth, be accurate, and keep their independence. While there is no such thing as total objectivity, in that every reporter has their own values and opinions, most reporters do strive for objectivity, fairness, impartiality, and balance. The mainstream media acts as a watchdog for corruption and scandal regarding both Democrats and Republicans and for the most part they do a good job of it. Sure they make mistakes, but they serve a vital public service. Reporters see their work as a noble and important profession and take their jobs seriously as far as being fair and accurate.

Republicans often repeat the liberal bias mantra any time they are posed with tough questions or negative coverage. Its a way of working the refs to try to get positive coverage.

Reporters and debate moderators do not shy away from controversies involving Democratic and Liberal politicians. They cover Liberal scandals as well as Conservative scandals. For example, during this years Democratic debates, Hillary Clinton was asked whether she could be trusted, whether she lied to the Benghazi victims families, whether she would drop out of the race if she was indicted about the email scandal, and whether she would release the transcripts of her Wall Street speeches. Bernie Sanders was asked about his past praise of Fidel Castro and how any kind of socialist could win a general election in the United States. The New York Times and other major newspapers have subjected Hillary Clinton to tough scrutiny over the years. Most recently, the mainstream media has criticized her for not holding press conferences. As noted in my book, there are many other examples of tough media coverage of Liberal and Democrats, such as the coverage of President Clintons marital infidelity and President Obamas connections to Rev. Jeremiah Wright.

In order to demonstrate the concept of Advocacy Journalism, I have my Journalism students watch one Fox News Show, such as Sean Hannity, one MSNBC show, such as Rachel Maddow, and one episode of the Nightly News on NBC, ABC, and CBS. The students general consensus is that the Fox News shows have a conservative bias, the MSNBC shows have a liberal bias, and the network nightly news is primarily objective, fair, balanced, impartial and neutral. Unlike the cable news shows, the network nightly news presents both sides of the issues in an even handed manner and the host has a neutral, non-judgmental tone. In contrast, Advocacy Journalism outlets, both Liberal and Conservative, report the news in an opinionated and adversarial manner. This occurs on Fox News, MSNBC, talk radio, which is mostly Republican and Conservative, as well as various Liberal and Conservative websites, blogs, and You Tube and Internet Radio programs.

If you compare these Advocacy Journalism outlets to the mainstream media, youll see that the mainstream media is much more objective, fair, balanced and impartial than the reputation that Donald Trump and Republican Conservatives portray. There is no such thing as perfect objectivity, but most reporters do a good job of being fair and impartial. In this respect, their fairness trumps their negative reputation.

Larry Atkins is the author of Skewed: A Critical Thinkers Guide to Media Bias (Prometheus Books). He teaches Journalism at Temple University and Arcadia University. Twitter: @larryatkins4. Email: larryLTatkins@aol.com

This is an updated Op-Ed that first appeared in WHYYs Newsworks.org