Danielle Allen is a political theorist at Harvard University and a contributing columnist for The Post.

In the fall an old book, called “On Duties,” by Cicero, the Roman statesman, philosopher and orator was exceptionally helpful to me. I taught the history of ancient political thought, and in the sessions before and during the election, we read Cicero.

Truth be told, until this year, I had always found “On Duties” the most boring book ever. That changed this year. In November, reading Cicero’s steady, even, unchanging prose against the backdrop of the frenzied froth of our own politics, I finally got it.

Cicero was a Stoic, someone who insisted that happiness lay in not letting emotional tumult rule one’s existence. The boring simplicity of his prose is not an accident, not an instrument for torturing students. It’s a bravura performance of Stoic equilibrium.

The ancient Roman dictator Julius Caesar was assassinated a mere six months before Cicero wrote “On Duties.” The leading Roman politicians were vying to master the power vacuum left by Caesar’s demise. No one closely involved in Roman politics was safe in their person, possession or loved ones. In fact, Cicero himself would be killed in little more than a year. In the wake of Caesar’s assassination, he had retreated to his country house and sought to write.

Thus emerges “On Duties,” a performance of calm amid chaos, of commitment to virtue and self-mastery amid bloodthirsty violence. In this performance, Cicero reminds us that the first step out of chaos lies in our individual ability to find a stoic equilibrium, a strength of will that protects us from being buffeted by storm and scandal. Steady in our own mind, we can keep our eye clearly on the goal. Cicero’s goal was recovery of the Roman Republic. Our goal should be the achievement of an indivisible America with liberty and justice for all. He failed at his goal. We may still hope to succeed at ours.

The purpose of stable political institutions and constitutionalism is to concretize habits of calm deliberation and stately decision-making. Our political institutions are meant to temper the heats of factionalism and to counteract passion’s erratic impulses.

“On Duties” is not boring, it turns out, but breathtaking. Read “On Duties” now, keeping in mind the turbulence of Roman politics, and let yourself be suffused with awe. To be calm in chaos is an epic achievement. For us, too, these aren’t ordinary times, and in such times the first step toward beating back disabling turbulence is finding the steadiness of mind necessary to keep control of one’s own agenda.

Donald Trump’s scattershot fire-setting serves a political purpose. It sets those who would hold him accountable constantly chasing after another potential crisis, unable to set their own agenda. Time and talent are consumed figuring out which of his many surprising pronouncements merit attention. The carefully crafted atmosphere of uncertainty keeps everyone on the back foot, playing defense, trying to clean up messes, or prospective messes: a new nuclear-arms race, capitulation to the Russians, a dramatic and unprepared resetting of the conversation with Taiwan, and so on. As Trump sparks firestorms of wasteful emotional energy, the conflagration of talent adds massively to history’s ash bin.

(D.C. Superior Court)

In this environment, we would all benefit from some Stoic equilibrium. Who cares if presidential access helps Ivanka Trump sell jewelry? Who cares if Donald Trump ditches his press pool to play golf? Our talents, energies and commitment are needed for more important work than fending off kleptocracy or even knowing where Trump is at all times. It’s okay not to respond to every single startling thing.

To repeat, we need a clear eye on the goal of an indivisible America with liberty and justice for all.

Might we perhaps begin the pursuit of Stoic equilibrium by disregarding any and every tweet by Trump? Let none of his words count until they issue through the formal channels of political institutions. If he can’t get his words and views expressed through Congress, through the White House press secretary, through official White House statements, they don’t merit our energies. Let’s redirect our time and talent from scrutinizing those tweets to setting a positive agenda.

What, we may ask, would it take to achieve America indivisible with liberty and justice for all? Democrats, what are you doing for that cause? Congressional Republicans, how about you? Let’s start by talking about health care. What’s the positive picture here? Anyone, anyone?

I’ve got my eye on America Indivisible, the true goal, and for that clarity of focus, I thank a most unlikely benefactor, the Roman politician Cicero.