I see denial as being on a spectrum ... not necessarily a negative response, and on the other end, rendering us incapable of growth.
Denial and coming out of it is about what we choose to pay attention to. What we allow ourselves to see, and when, and to what degree.
It can be self-preserving.
The 'inability to be honest' with oneself... I always took this to be about those who were in full-on psychotic breaks with reality. And more about what constitutes reality than an inward, subjective honesty. And even then, the schizophrenic is being honest with himself in the face of what is real to him.
Are there irredeemable people? Psychopaths, maybe? Are these people being dishonest? Or are they just potentially very dangerous to the rest of us?
Is Trump incapable of it? Pushed to his breaking point, I bet he'd get honest, if only temporarily.