"The question to wrestle with is this," she writes. "Whether the president’s constant, intentional, derogatory statements and other hostile activities with respect to the press are consistent with an ability to fulfill, and fitness for, his constitutional role as commander in chief. I think they are not."
It's obvious why Trump attacks the mainstream press. They expose his incompetence, his hateful behavior, and his many lies.
A free press makes it more difficult for Trump to peddle his falsehoods to his supporters. He's trying to create the illusion that he's succeeding brilliantly and isn't a bit corrupt, even though the opposite is true. And the press keeps saying the emperor is wearing no clothes.
He's borrowing this strategy from Richard Nixon and a lot of dictators and running with it. The problem is, unlike in the Nixon years, there are a lot of right-wing media outlets that are only too happy to peddle Trump's lies.
Sadly, too many people believe Trump because of the propaganda outlets masquerading as the press. Those folks don't sample a lot of media and, instead, watch and listen and read only one outlet. The result is like something out of George Orwell.
The writer of the linked piece has a fantastic conclusion, which I'll quote in its entirety here:
"While we don’t know the precise motivation for the president’s attacks on the press, what we do know is that they are deliberate. They encourage an environment of hostility against the media. They are intended to affect the press’s exercise of its rights under the Constitution. The attacks may be an effort to centralize power and dissuade further scrutiny of unscrupulous activities. And they are inconsistent with a constitutional role of protecting national security."