Even for the few intelligent Trumpers (and, frankly, I'm not sure there are any).  First of all, this country has a long history of ignorance and fear, especially in reaction to new immigrants.  Google the Know Nothings.
Second, a lot of it is connected to people in this country -- both on the right and on the left -- who feel betrayed by their own government and the political class that benefits from it.  They wanted someone who would tear up the system but they voted for the wrong person, even though Trump was the only choice if you really wanted the destruction of our government.

It is like being president requires one to be well versed at three-dimensional chess and Trump is barely able to play checkers.

The most complicated matters often have several layers of logic one needs to apply before making a decision.

As far as a decision concerning transgender members in the military is concerned, this is especially true.  Regardless of one's political affiliation or view on this topic, to just tweet a position on this is beyond irresponsible.  Imagine the impact this statement alone has on our military leaders, and all military members, not to mention numerous regulations, and personnel/recruitment plans.  These things take an inordinate amount of time to conceptualize and then implement.

Again and again, he says and does things without truly understanding the impact of his words/actions.  How can he be the intelligent, well educated person, he purports to be?