President Trump initially said the media didn't report some terrorist incidents, which was quickly clarified to mean that they underreported them. The New York Times released a long list of terrorist attacks they had covered in their reporting to counter Trump's claim.
The Times was correct on the very narrow question but totally wrong on the underlying truth.
No one questions whether the Times, and the media, have reported most terrorist attacks. They have. But they report on terrorist incidents the way they report the weather. It is brief, to the point, and usually gone the next day. Most importantly, there is never any examination of the "why" behind terrorist attacks. The Times simply reports "A man shouting 'Allahu akbar' went and killed three people. He is now in custody," expressing no greater interest in what caused the incident than what you would see about what caused rain on a particular day.
The underreporting that Trump is referring to is that total lack of curiosity on the part of the media about the motivations of the attackers. From that list the Times provided, you can see there have been many, many terrorist attacks by Muslims. Why are they committing so many attacks? Is this part of some trend that should concern us? The Times doesn't know and doesn't want to know.
Contrast that with the story of how a private security guard shot and killed a black man who was trying to pound his head into the pavement. The Times published literally dozens and dozens of articles exploring the possible racist motivations of the security guard. Every time a police officer shoots a black man (which, in a nation as large as 300 million people, can happen from time to time), the Times empties a well of ink trying to draw larger conclusions about the racism of the police.
Not so with radical Islamic terrorist attacks. There are no days and days of follow-up about the ideology that drove an Islamic terrorist. It happened, it's over, that's it, like a passing raincloud. That's the underreporting I believe President Trump is referring to.
And then there is the over-reporting that President Trump did not mention. For every story that dutifully reports a terrorist attack, there are ten or twenty stories highlighting the plights and virtues of Muslim refugees. They even fall into predictable categories:
1) The refugees who are just like Americans. They are constantly described as having Barbie dolls or wearing Disney shirts (the children too young to wear a burka) and as loving American food and supermarkets. If they like our supermarkets, they must be good, right?
2) The little things that humanize them. The story I reported on yesterday about Christians donning hijabs also showed a photo of a Muslim family eating a traditional meal. Eating food makes them appear non-threatening, like ordinary people. I remember one phrase from an NPR story where they talked about Muslim refugees who "goofed around in jerseys." Why was it important to say that Muslims "goofed around in jerseys"? It was part of the subtle propaganda to make them appear friendly.
3) The medically ill Muslims. Another class of story talks about the Muslims who need to come to America for medical treatment. Left unsaid is who is going to pay for it.
4) The split families. Another group of articles talks about some refugees who cannot feel whole until their entire extended family is in America. Left unexplored is whether the next round of refugees will want their relatives as well and where it will end.
5) The doctors, scientists, Ph.D. students. Trump's temporary travel ban has seemingly stranded an entire class of people with advanced master's and Ph.D. degrees outside the U.S. This is repeated over and over on the theory that highly educated people would not hurt anyone.
6) The feeling of persecution and victimization. Refugees in America are described as living in some Trump-inspired fear, though what it is exactly they fear is always left unclear. Presumably, they feel safer than the places they came from.
When you combine the underreporting of the causes and extent of Islamic terrorism with the over-reporting of Muslims as oppressed, deserving, virtuous people, there's your media bias. So the media can smugly say they have reported every knifing, every bomb attack, and still be wedded to a pro-Islamic and anti-national security bias in their reporting.