LBJ: a president who had skills that both Obama and Trump lack
Aristotle is an infallible guide to good politics - witness his wise observation that the most stable societies have a large middle class.
He is also convincing on what makes a great political leader: the virtue of political prudence.
By prudence, Aristotle does not mean caution but a golden mean between idealism and cynicism.
Neither Barack Obama nor Donald Trump pass that test. But Lyndon B Johnson did, albeit with tattered rather than flying colours.
Both Obama and Trump are at extreme ends of the bent bow of politics, with LBJ resting like an arrow of action between them.
Aristotle has no time for either impotent idealism at one extreme, or selfish cynicism at the other end.
He believes a good leader should aim for a pragmatic idealism, going for the greatest good compatible with constraining circumstances.
Accordingly, a politician who wants to achieve a great aim may have to do some grimy things along the way.
Winston Churchill had to bomb the French fleet at anchor to prevent it falling into Nazi hands. Michael Collins had to fire on his former comrades in the Four Courts.
Both actions were necessary to achieve noble ends, but neither actions were noble in themselves, and open to criticism.
Obama is a perfect example of one extreme: the idealistic but politically impotent leader who would not have impressed Aristotle.
At a personal level he is clearly a more admirable man than Trump.
But these personal virtues, which include inhibitions about the use of force, did not help him be a great president.
Conversely, Trump's natural aggression may be an asset in certain circumstances where America faces foes who are testing its mettle.
As we have no crystal ball it is too early to say that Trump's presidency will turn out to be the total disaster that increasingly hysterical and irresponsible liberals seem to be hoping for.
But Obama has nothing to boast about. At home, he failed to build a crucial coalition of the white and black working class, an alliance he was well fitted to accomplish.
Abroad, his dithering has damaged the status of the United States, and not merely in the Middle East.
These failures stem from the fact that Obama is that most tragic of figures, a personally good man who is not willing to make the tough calls that come with his great power, or face the results of force close up.
Thus he was able to send drones to kill at a distance where the deaths are out of his sight and mind, but not able to send planes or troops which might incur all too visible American casualties.
Aleppo is the tragic result of his reluctance to use the full power of America to protect the rebel Syrians against Assad.
Obama cannot dodge the moral consequences of his inaction which amounted to inciting the rebels and then letting them down.
He didn't mean it when he issued his infamous "red-line" warning to Assad - that he would attack him if he used chemical weapons against his own people.
Obama has the politics of a liberal college professor. Like many liberals, he is not comfortable with military power, even for good ends.
He has never been committed to the noble notion that America is a world cop, the court of last resort for those who have no other resort.
If you seek his monument look at the ruins of Aleppo, the sad symbol of the death of American influence in the Middle East.
The Russians pulverised it from the air, doing for the Assad regime what Obama could not face doing for rebels whose hopes he had initially raised.
Aleppo bled civilian dead, while America, once the coercive power in the region, stood idly by and wrung its hands.
Obama could have done many things to slow down Assad, far short of putting American troops on the ground.
He could have set up no-fly zones to stop Syrian helicopters dropping barrel bombs on their own people.
He could have established safe houses for civilians and policed the skies above them with American planes.
But he preferred to lay back in his political rocking chair, wringing his hands, making pointless speeches to his captive audience of adoring liberals.
Turning to Trump, at the other extreme of Aristotle's bow, we are confronted not by a waffling idealist but by a blustering cynic.
At home, I doubt his protectionist policies will deliver the promised jobs to the poor devils of the Rust Belt who voted for him.
But he may do some good abroad by making the Russians ponder the wisdom of throwing their weight around in Western Europe.
On balance, I believe Trump will do less harm than Obama.
But the current left liberal media campaign against him is out of control and will not help to calm the body politic.
The left liberals like to pretend that Trump is a fascist monster, something like Mussolini, if not Hitler.
Actually it's more likely Trump will turn out to be a Charles Haughey, a potential tiger in exile but a toothless tabby in power.
Leaving aside laid-back Obama and too-forward Trump, let's look at a US president of whom Aristotle would have approved.
Lyndon Baines Johnson was a perfect example of the pragmatic idealist, a president whom many liberals did not like, even on personal grounds.
LBJ had rough personal habits, using foul language and sitting on the lavatory with the door open while lecturing his hapless aides.
But he knew that politics was about power. And he believed power should be wielded on behalf of those who had no power.
Jonathan Darman, in his book Landslide, gives us a gripping picture of how LBJ used even his body to make political points.
"He made use of his large girth and six-foot-three-inch frame. All the cliched metaphors of politics - glad-handing, buttonholing, back stroking, arm twisting - were things Johnson actually physically did in order to get his way."
George Wallace, the racist governor of Alabama, pithily summed up the power of a one-to-one session with LBJ: "Hell if I'd stayed in there much longer, he'd have had me coming out for civil rights."
Johnson's two great achievements were civil rights and the social welfare legislation that comprised his 'Great Society' policy.
Taken together, they leave the legacies of Bill Clinton and Obama looking lacklustre and lacking in ambition.
But they were the product of a relentless idealism backed by brutal political blackmail, especially in the prodigious effort to secure civil rights.
Early in his career, LBJ had shown he could push modest civil rights laws through the Senate.
So when he came back with a bigger package of civil rights after 1964, he was sure he would succeed this time, too.
As he pointed out crudely: "Once you lose your virginity there's nothing to stop you doing it again."
Johnson correctly predicted that pushing through civil rights would destroy the Democrats for a whole generation in the south.
But he, a Texan, was still willing to pay that price. For that, Aristotle would have forgiven him the lavatory lectures.