Sources have always been critical to providing legitimate news stories. Vetting sources, fact checking, and verifying the credibility of the information they provide is a basic, necessary function of any professional journalist. In today's 'instant news' culture, this skill and virtue has been lost. Journalist rush to be the first to break a story and grab the spotlight for themselves and their news organization. In the rush, verification is often neglected because there are rarely real consequences for irresponsible journalism. Retractions are posted several days later, buried deep within the paper or at the bottom of an online post.
Clearly, in the example, President Trump uses inflammatory, strong language and the degree of his critique is far too strong. At the same time, the point he makes is an important one. News sources must be vetted, trusted, and legitimate. If they are not, the news itself is not news at all. It is merely biased-stained gossip.