The following is an excerpt from the Op-ed in the New York Times of Sept. 5. What does the author mean by "I would know." towards the end of the quote?
"President Trump is facing a test to his presidency unlike any faced by a modern American leader.
It’s not just that the special counsel looms large. Or that the country is bitterly divided over Mr. Trump’s leadership. Or even that his party might well lose the House to an opposition hellbent on his downfall.
The dilemma — which he does not fully grasp — is that many of the senior officials in his own administration are working diligently from within to frustrate parts of his agenda and his worst inclinations.
I 〈would know〉. I am one of them."