Tomorrow will mark three weeks since the Newtown, Conn., school massacre. The wretchedness of that day has touched off a national debate about preventing mass murders -- as it should. But lately the conversation has narrowed to gun control.

In a year-end interview, responding to a question about the political fights ahead, President Barack Obama voiced his support for banning assault rifles and high-capacity clips, and for better background checks for gun buyers. What I didn't hear from the president was a vow to strengthen our mental health system to treat people like Adam Lanza before they descend into madness. Whatever Lanza's technical diagnosis -- schizophrenia? -- executing two classrooms of first-graders is by definition mad.

Gun control is easier to discuss, because there is an identifiable, organized opposition in the National Rifle Association. But mental illness is harder to recognize, reach and heal.

Consider the divergent responses I received to a column that ran right after the Sandy Hook killings. I wrote that in New York, as in most states, the law allows for involuntary commitments of those who are mentally ill. What's more, New York permits someone to alert the authorities to dangerous behavior while remaining anonymous.

Some readers wondered about the potential for abuse of involuntary commitment -- also called civil commitment. "How do [the authorities] know that you are just not furthering a neighborly feud or personal vendetta?" one man emailed.

Others said that even though such laws exist, they are almost unenforceable in practice. A mental-health group home administrator said he has often been frustrated when calling for help: "There is no mechanism for involuntary admission unless the person is either violent or expresses violent ideas in front of a psychiatrist or police."

And so there is the conundrum. The problem isn't the law, exactly, but the judgment, resources and political will to enforce it.

We have yet to find the place where the pendulum should rest since deinstitutionalization began in the 1960s. The idea was to wipe out the abuse of mentally ill people, to respect their civil rights by closing psychiatric hospitals and moving toward community-based care, such as group homes and outpatient treatment. But the system that was supposed to take the place of psychiatric hospitals has never been adequately funded or built out.

The results are cruelly inadequate. Twenty percent of prison inmates, and at least one-third of the homeless, are seriously mentally ill, according to the national Treatment Advocacy Center. Mostly, they are not receiving the care they need to heal, stabilize and lead full lives.

And, as appears to be the case with Lanza, responsibility for care falls to individual families -- sometimes with disastrous results. In two other recent mass murders -- the killing of 12 people and injuring 58 at a Colorado movie theater in July, and the wounding of Rep. Gabrielle Giffords and killing of six others in Tucson two years ago -- family, acquaintances and school officials had been alarmed about the behavior of the two men who became suspects. Yet no one stopped them.

Most mentally ill people are not violent, but statistics favor stronger civil commitment laws. According to a 2011 study by the University of California, Berkeley, states with stronger laws have homicide rates about one-third lower.

Vice President Joe Biden is preparing a report on preventing mass shootings. If he wants a place to start, he might consider our patchwork of state civil commitment laws -- both how they are written and how they work in practice.

This essay was first published in Newsday.