Trump famously embodies the
Dunning-Kruger effect, whereby people who know very little about a field think they know much more than they actually do. He is also the walking embodiment of
H.L. Mencken's maxim that complex problems have simple, easy to understand, wrong answers.
That is, of course, a major source of his appeal. He appeals to people who don't know any more about policy questions than he does and assume that there are simple solutions out there that politicians have not adopted because they are too stupid, corrupt, or weak-willed. Trump claims that he will cut through the red tape and fix everything by not being half-hearted about it. Of course, when his profoundly ignorant claims run up against reality, things tend not to go so well.
In his first term, Trump appealed to people's complaints about Obamacare. "We'll have great health care at a fraction of the cost and it will be so easy." It was, after all, what people wanted to hear. After working on it a while, Trump complained, "Who knew health policy was so complicated." Not many people, Donald, just anyone who knows anything at all about health policy. Admittedly, this is a fairly small portion of the total population. He ended up with a plan to repeal Obamacare with no replacement and thereby strip 20 million people of their health insurance. I think even the least informed members of the pubic would have noticed that.
Much the same applied when Trump agreed to a summit with the North Koreans. He only cared about the pomp and pageantry and was not interested in trivial details like what agreement they might reach.
For his second term, Trump promised to end the war in Ukraine in one day. Presumably he believed that his friend Pooty, would happily end the war as a personal favor. To the extent the Ukrainians were unwilling to agree to Putin's terms, a little arm twisting should bring them into line. Well, this failed for much the same reason -- Trump thinks of foreign policy solely in terms of personal relationships and has no idea that countries have interests that transcend the individuals in charge.

So too with the Iran war. The Iranians' clear wish up until February 28 to avoid war with a much stronger country made Trump think they were pushovers and easily intimidated. What he didn't understand was that the regime was never going to agree to its own destruction, or that it would fight fiercely when cornered, although both points should have been obvious. He appears to have believed that Iran would be intimidated into submission by the mere presence of US forces or, failing that, that he would have been able to swap out the name at the top for someone more compliant, just the way it has worked in Venezuela.
When that failed, Trump's advisors apparently convinced him that if he blockaded the straits, pressure would build up in Iran's oil storage and threaten to blow up in a matter of days, which would presumably force their capitulation. Well, spoiler alert, that didn't happen either. Trump now seems to believe that if he threatens and cajoles enough the Iranians will agree to his terms in a matter of days. He has no patience for the long, drawn-out process of diplomacy.
In the case of Obamacare, the dying John McCain made one last appearance in the Senate to save his party from itself and vote down repeal. No deal was reached in either Korea or Ukraine, so the situation continued -- bad, but ultimately something most Americans could live with.
Well, the war in Iran is looking to be the most intractable problem yet. Continuing that status quo is clearly not acceptable and bound to get worse, but there is no easy out.
Maybe next time don't elect President Dunning-Kruger.