Could President Trump be any more incoherent on policy? It's hard to see how.

From the beginning of his presidential campaign and all the way through the election and transition, Trump displayed hostility to constraints of any kind — rules, institutional norms, ideology, party loyalty, and all the expectations that normally attend to presidential nominees and office holders. Now that he's president, this refusal to be pinned down has transformed itself into a jumbled, incomprehensible mess on both foreign and domestic policy.

This is a president who once eviscerated his predecessor for meddling in Syria but has in a matter of days undergone a complete reversal and decided to lob a few dozen Tomahawk missiles at Assad; who ran as a populist but who also wants to cut taxes on the rich; who mercilessly attacked Goldman Sachs but then tapped several prominent people from the investment bank for his Cabinet and other senior positions; who promised no one would lose health insurance when ObamaCare was repealed but then pushed a bill that would have left 24 million fewer people insured; who spent two years denouncing existing free trade agreements but now can't decide whether to break with existing trade policy.

On policy, Trump is a fool and an incompetent the likes of which the United States has never seen.

That's bad for all sorts of reasons. It means that many of Trump's already angry supporters are likely to end up feeling betrayed and (even more) bitterly disappointed. It means the government could be hamstrung for much of the next four years as the president careens haphazardly from one priority and position to another. It means that the U.S. may find itself embroiled in yet another war (or two) that no one had any reason to expect.

But perhaps most ominously of all, it means that our president has the instincts of a tyrant.

There's nothing inherently wrong with a president displaying a willingness to be flexible. In fact, politics at its peak involves acts of prudence or practical judgment that transcend the rules that normally prevail in political life.

This is a lesson nicely conveyed by the amusing tale of the two coats from Xenophon's Education of Cyrus. In his account of the Persian emperor's youth, Xenophon tells us that one day the future Cyrus the Great saw a big boy wearing a small coat and a small boy wearing a big coat. When the big boy took the small boy's large coat and gave him his own in return, Cyrus judged that this was a just result. For this Cyrus received a beating from his teacher, who indicated that Cyrus should have enforced the law against theft by returning each ill-fitting coat to its rightful owner and punishing the bigger boy for stealing.

But of course Cyrus' original instincts were right. The laws or general rules we live by (like that theft is illegal and stolen property should be returned to its owner) are good in most circumstances. But not in all of them. In the case of the two boys, each would have been better off with each other's coat, so the act of stealing was justified. Not as a general rule, but in this particular case.

Politics on the highest level requires precisely that kind of practical wisdom and flexibility. The statesman needs to determine whether and when the common good demands a shift in policy, and perhaps even the transgression of the norms, rules, expectations, and laws that normally abide. He needs to be capable of making a call about what's right and wrong in particular cases and circumstances, and to adjust accordingly.

Trump's resistance to being pinned down and his continual shifting of policy ground points in this direction. He doesn't want to be told what he should or must do; he doesn't want to feel like his freedom of movement has been constrained by anything external to himself. He has absolute faith in his judgment and wants to make all the calls on his own based on what he thinks is right at the moment.

The problem is that Trump shows not the slightest sign of possessing the prudence required to make such judgments with intelligence. He's impetuous, vindictive, vain, motivated above all by a craving for popular adulation, incapable of reading more than a few words at a time in a briefing memo, and proudly ignorant of the details (or even broad outlines) of both domestic and foreign policy. He doesn't even know how long he's been president. He's a fool.

When a political leader prizes flexibility but lacks practical wisdom, what you have is an incredibly powerful person who does whatever he wants. That's a recipe — the classic recipe — for tyranny. Especially when, as in Trump's case, the leader is motivated above all by insatiable longing for public approval.

Thankfully for us all, the presidency (though a mighty position) is embedded within a much larger structure of government that limits and checks its powers. It's hemmed in on all sides — by Congress, by the courts, by the federal bureaucracy (including the intelligence community), by the press, by public opinion, by the logic of each party's ideology and electoral coalition. Trump appears to bristle at these constraints, but he can't will or wish them away.

Still, he's testing them as they've rarely been tested before. By the time it's all over, we will have learned whether they proved capable of containing the capricious will of a would-be tyrant who yearns to do anything he wants but utterly lacks the capacity to do so wisely.