Nor is the history of the news media been all that great. In some cases, it has been hijacked as a propaganda machine for the government; in others, it has attacked immigrants, minorities, and other powerless sectors of our society as a way to further cement the power and wealth of a few (who often owned stake in the news agencies). From muckraking to yellow-journalism to censorship, our media's hands have never been clean. Even Spider-Man is plagued by J. Jonah Jameson.
Thus, when a politician starts talking about "fake news," people are willing to listen. Suddenly, the lack of trust that has been built over the years rains down on our nation's news agencies. Because they misled people so often, now, even at those times when they hold entirely to the truth, many people don't believe them.
Unfortunately, politicians claiming "fake news" are now doing so to cover up their own faults and failings. People are willing to believe them because they want to believe that they haven't been duped. I've seen over and over again people posting that they don't know who to trust or what to believe anymore. Honestly, I'm more scared of those who fanatically believe any source of information.
In many ways, I blame this on the modern concept of relativism that has pervaded our world in the past few decades. The claim is that truth is in the eye of the beholder. I do not believe that there are multiple truths, but one Truth that is seen from multiple views. We need to work as individuals and as a society to seek that Truth, and stop believing lies because they are more convenient.