My small contribution to this eternal debate: We can distinguish between "lie" as a noun and "lie" as a verb. Something can be a "lie" without knowing if the person saying it is "lying."
Example: "The Holocaust never happened" is a lie, even if the person saying it believes it.
Example: "The Holocaust never happened" is a lie, even if the person saying it believes it.
As done by @nytimes here: The statement is a lie, regardless of Trump's state of mind. 
Both sides make good arguments here! Journalists know interpreting a mental state is dangerous and opens them up to criticism, both well intentioned and not. And those who complain don't see why "he might just be delusional, not lying!" serves as a get-out-of-jail card.
So maybe let's call a *statement* a lie when it is demonstrably, incontrovertibly false, or when it has been repeatedly shown to be completely unfounded. And then we can leave the psychoanalysis to the pros. /end
Update a day later: Everyone critical of @maggieNYT in this thread should at least read this new piece to be fair nytimes.com/2018/05/28/us/…
