It is not just 'claims' that Trump is irrational and inconsistent. Trump's actions are cause and confirmation of these claims. You extend these valid claims of Trump's irrationality and inconsistency by inferring that mr. Harris (we are not on first name basis) wouldn't "find Trump such an a..hole if only he were logical and consistent". That appears to be a stretch. Inferring that Trump would be more easy to understand is all we can do, specifically since you quote mr. Harris as saying "Osama Bin Laden [...] is far more understandable to me and far less reprehensible to me personally, psychologically, than Trump" . Keywords: understandable, personally, psychologically. Understanding a murderer doesn't mean justifying his actions. And that is the leap that you appear to be making.
You then attempt to make the argument that the outcome is somehow the determining factor in how we should evaluate the person: "If rationality does not help in the survival of the species, it is not rationality", and "time tells the results of our thinking". I don't understand this. Let's take an example: If we, concluded after research, tests, and investigations that Covid-19 will decimate not only the human species but also many other species and we decide to vaccinate against it, then find out that it doesn't work, then it wasn't a rational decision?
If in poker you hold a full house and the actions of the other player are consistent with bluffing and the chances of her having a stronger hand are minimal, shouldn't you call the bluff, all other things being equal? You should, but you can still lose.
Rationality allows us to increase the probability of making the right decisions. The right decisions being those that have the best chance of positive outcomes.
If we do not use rationality, but flippant remarks, such as "that virus will just magically disappear", as the basis for our decision-making, then we will run into each and every possible disaster. This flippancy and disdain for this key human quality, the capacity to think beyond our immediate reflexes, is what makes rational people (a category I have some difficulty with, but let us assume that we mean people who are well trained in critical thinking and are able to use it to make cogent, valid argument, but who do not have to be infallible) very uncomfortable with Trump. I would accept that mr. Harris would feel uncomfortable with Trump's flippant, inconsistent, poorly thought through claims (as I haven't heard him make many arguments, based on hypothesies, logic and conclusion).
Rational people feel that they, and humanity as whole, are taken hostage by narcissistic behaviour. They feel disoriented because no reasoning, no argument and no evidence finds any foothold for having a conversation, let alone an intelligent one. Claims by Trump and his followers, no matter how absurd, have become the basis for decision-making. The Enlightenment, Science and Reason, what we learn, how we improve, it's all out the door, in favour of magical thinking, spurious claims and dangerous ideas. That is what Trump represents.
The difference between Trump and dictators/terrorists is that Trump thinks he can say and do anything he wants without consequence, whilst these tyrants have ideals, however misguided, and act accordingly. The actions of tyrants/terrorists can often not be justified (but they are to some degree in the case of the French and the American revolution), but they can be understood in light of their beliefs and objectives. Trump's actions cannot be justified AND cannot be understood because they are not based on a cogent set of beliefs or objectives. That said, some of his actions and objectives could actually be justified, whether you agree with them or not.
