People hold candles at a vigil Saturday in the aftermath of the deadly shooting at the Tree of Life synagogue in the Squirrel Hill neighborhood of Pittsburgh. (Matt Rourke/AP)

Should the Tree of Life synagogue in Pittsburgh have had armed security? President Trump suggested this in his response to Saturday’s horrible tragedy. The moral blindness of this view is severe.

The moment is one for mourning deeply. But it is also well past time to see clearly.

Once upon a time, a first-order goal of building civilizations was to reduce the need for weapons in daily life. The point of politics was a domestic peace sufficient to dispense with the ordinary carrying of arms; weapons were assigned the job of securing safety from external threats. Once upon a time, the purpose of sound democratic political institutions was to ensure domestic tranquility while also providing for the common defense internationally.

My first “once upon a time” refers to the democracy of ancient Athens. My second “once upon a time” refers to the era of the U.S. Constitutional Convention.

Thucydides’s “History of the Peloponnesian War,” which recounts the 5th century BC clash between democratic Athens and oligarchic Sparta, is still taught in international relations classes. It introduces people to realist views of foreign policy and balance-of-power analyses of conflict. Yet even Thucydides thought that the goal of domestic politics was a peaceful society where citizens would not need to protect themselves on a daily basis with weapons.

He opens his book by explaining how Athens had become a great city. He writes, in Rex Warner’s translation, that once “throughout the whole of Hellas [it was] the normal thing to carry arms on all occasions.” But then Athens, with its strong political institutions, achieved a new state of affairs. “The Athenians,” he writes, “were the first to give up the habit of carrying weapons and to adopt a way of living that was more relaxed and more luxurious.” They were able to spread this transformation through Greece with the result that, the habit of carrying weapons at all times could now be found only “among foreigners.” From Thucydides’s point of view, this was a tremendous achievement on the part of the Athenians. It paralleled the eradication of piracy.

The notion that we should have to arm ourselves on a daily basis in order to be free from persecution is to propose that our lives together are characterized by war, not peace. It is to abandon the commitment to building a society where people are free from persecution. To need to carry weapons, as a matter of course, to protect oneself against one’s fellow citizens is not an acceptable definition of domestic tranquility.

We are committed through our Constitution to ensuring our domestic tranquility, and we are not achieving that. What would it take for us to do so?

I believe at least three things are necessary first steps.

One. Our leaders, all of them, from both parties, need a change of heart. They need to ask themselves what it would take to bring peace among us, a peace that includes all of us. They need to make peace among us an actual, actionable priority. They need to make this a matter not of producing supposedly unifying platitudes in the wake of crisis but of an alternative strategy of governance, one that includes compromise. Where they do not make peace among us a priority, visible in their methods of governance, we the people should hold them accountable for that by voting against them.

Two. We need regulations for gun ownership that restore guns to their appropriate place in a civilized society. They should be regulated to limit their use to hunting and leisure — a reasonable part of a world where we are able to be on relaxed terms with one another.

Three. We need a national health-care infrastructure that makes meaningful mental-health resources available to all and, more generally, establishes a foundation for thriving for the entire population. Everything goes better when people have access to health care — education, work, relationships. Our fragmented system, which leaves so many without protection, spreads stress and anxiety, contributing to the phenomenon of social despair now well-documented by economists. This social despair is surely one source of our violence within.

What is domestic tranquility? It is not being gunned down in your house of worship. It is not being gunned down in school. It is not being gunned down at a night club or concert or baseball field. Nor is it having to carry a weapon to each of those places.

Achieving domestic tranquility is a constitutional issue. It is a moral issue. It is a matter of what, without discrimination in regard to our social identities, we all owe one another. It was what we owed — it is what we still owe — each blessed, beloved person lost or harmed at Tree of Life.