I am open to an argument defending Trump but the list you have provided is not evidence.

- "the source is anonymous" does not refute the existence of the memo. Credible reporters have verified the source and have corroborated the it.
- "no one has seen any memo" - Comey's FBI associates have seen it. This was apparently his way of ensuring the truth was recorded and dispersed widely enough there could not be a cover up (e.g. Watergate).
- "the White House denies it" - really? The White House consistently lies. They are no longer a credible source of any information.
- "Comey has not affirmed it" - true. But we expect he will when he eventually testifies.

So I disagree. This is objective journalism. 

It is sad to see the destruction of the Office of the President.

I am open to the argument that Trump is not a politician, reactionary by nature and he is not aware of the consequences of his actions. This is the best case explaination I can see.